The Laws of Body Inflation 1.1

Law of Induced Elasticity:  Applying gas under pressure to a person will dramatically increase how much that person's body can stretch well beyond what physics or biology would indicate is possible.  Any person can potentially be turned into a balloon.

Law of Sympathetic Elasticity:  Wearing balloon-like clothing dramatically increases the chances that a woman will herself become balloon-like.  The more stretchy and form-fitting the clothing is, the higher the risk.  An outfit consisting entirely of latex and/or spandex virtually guarantees that the wearer will inflate.  Nobody has ever inflated while wearing a muumuu.

Law of Spontaneous Pressure Inversion (The Blowback Effect):  As an inflatable object approaches its maximum capacity, the interaction of elastic material and human breath creates an extremely unstable situation.  There is a small but significant chance that the inflatable will suddenly and rapidly return to its uninflated state, instantly returning all of the air it contains to the person inflating it, rapidly inflating said person in the process.  This can happen with balloons, pool toys, or any other inflatable.

Law of Superfluous Complementary Functionality:  Any device which generates suction (e.g. vacuum cleaner, breast pump) will have a 'reverse' setting, despite there being no conceivable application for such a setting in the device's normal usage.  This mode will usually be engaged accidentally, and will almost always result in someone inflating.

Law of Exhalation Impairment: While being inflated via the mouth, people are incapable of exhaling through the nose.

Law of Deflation Infeasibility:  Now matter how quickly or easily a person inflates, the deflation process will be orders of magnitude slower, if it's possible at all.
First Corollary:  A person who has been inflated via the mouth will only be able to exhale one breath's worth of gas once the inflation stops.  Exhaling the rest will be impossible and the person will be stuck in an inflated state.
Second Corollary:  Any spell, potion, or chemical that causes inflation will have no countermeasure.  The victim will have to wait until the effect wears off on its own.
Third Corollary:  You cannot deflate a person by poking a hole in the skin to let the air out.  Puncturing an inflated person always results in explosion.
Fourth Corollary:  A person who has been inflated by almost any means may deflate quickly by exhaling if and only if the air is blown into another person.  Deflation is permissible if it results in inflation.

Law of Uninterruptible Inflation:  It is impossible to break any connection that's being used to inflate someone as long as there's gas flowing through it.
First Corollary:  A hose that's inflating a person cannot be disconnected.  Any attempt to do so will cause the connector to jam.  The hose will remain connected until the source of inflation is exhausted or shut down.
Second Corollary:  When a person who is blowing into an inflatable object experiences blowback, the inflatable's valve will remain stuck to that person's mouth until all of the air has been transferred.
Third Corollary:  It is impossible to break off a kiss while one person is blowing into the other.

First Law of Inflationary Resilience:  The human body can be filled with sufficient pressure to break free from any constraints.  Shirts, belts, corsets, and small residential structures can contain an inflating person for a while but will ultimately be destroyed.

Second Law of Inflationary Resilience:  The process of inflation makes human skin extremely sturdy.  The strain from bursting free of clothing or crushing furniture against the walls will leave no marks.  A person can destroy a small building and remain completely unscathed by the countless splinters, metal fragments and broken glass.

Third Law of Inflationary Resilience:  If the inflation is reversed, then the person's body will return to it's normal condition without experiencing any ill effects from having been inflated.  There will be no blemishes, stretch marks, aches, pains, or sagging of the skin.  However women often experience significant residual swelling, most commonly in the breasts and the hips.

Law of Inflationary Vulnerability:  Even though inflated people are immune to any environmental hazards, they can be easily burst by anyone with a minimally pointy object and malicious intent.  An inflated person who has survived demolishing a house without taking a scratch can be easily done in by a jab from a sharp fingernail.

Law of Disproportionate Response:  Inflating someone, even to the point of explosion, is an appropriate punishment for any perceived wrongdoing.  This is true even for the most trivial of offenses, real or imagined.  If your girlfriend cheats on you, breaks up with you, nags a lot, or chews really loud then you should feel perfectly justified in slipping some helium pills into her drink.

Law of Pneumatic Indemnification:  Never under any circumstances is it illegal to inflate someone.  Because there are no laws covering inflation, people can feel free to inflate others as they see fit with no fear that the authorities will get involved.

Law of Interruptive Detonation:  When a person explodes, it usually happens when that person or someone nearby is talking about how likely it is that the person will explode.  Anyone commenting that someone is about to explode is very likely to be cut off by that person doing so.

First Law of Situational Ignorance:  In the case of unexpected inflation, the victim will often remain unaware of his or her own inflation in progress.  The victim will ignore the inflation for as long as possible, dismissing it as imagined or attributing it to some mundane cause.  The victim will assume that tightening clothes must have shrunk in the wash or that a swelling stomach is the result of digestive problems, for example.

Second Law of Situational Ignorance:  Bystanders within sight of an inflating person will not notice the inflation unless that person does something dramatic to draw their attention to it, like screaming "Oh my god, I'm inflating!"  Popping buttons off of clothing, knocking over furniture, or exploding will also usually, but not always, attract the attention of bystanders.

Third Law of Situational Ignorance:  People rarely look up, and will almost always be oblivious to an inflated person floating overhead.  A person who inflates and floats away will simply be reported as missing; nobody will report seeing a strange balloon rising from said person's home around the time of the disappearance.  This makes inflation an ideal method for getting rid of people one finds annoying.

Law of Bystander Complacency:  Even once they become aware of a person inflating nearby, bystanders will rarely take action in response the inflation.  They will not offer assistance or call for help.  They won't even flee the area or seek to shield themselves from the impending blast when it appears likely that the inflating person will explode.  However they will offer plenty of comments, all of which will be completely unhelpful, one of which will probably be interrupted by an explosion.

Law of Ineffectual Intervention:  Any attempt to assist someone who is inflating will invariably be poorly conceived, incompetently executed, and/or carried out too late to be helpful.  At best, it will be completely ineffective.  But it's even more likely that any attempt to help will actually make the situation worse.

Law of Personal Puritanism:  The most compelling of human motivations is not self-preservation but modesty.  A person who is experimenting with inflation will have no concerns about bursting but will be deathly afraid of being seen naked.  Thus, anyone who plans on inflating will not do so before acquiring attire that will keep them covered while inflated.

First Law of Sensory Distortion:  The nerves which transmit pain are easily disrupted by the peculiar sort of tension stress that comes from internal pressure.  Once inflation starts, they shut down very quickly.  The the most unpleasant sensation an inflating person can experience is mild discomfort.

Second Law of Sensory Distortion:  As the skin becomes tighter, pleasure sensors move closer to the surface and the tension causes a dramatic increase in sensitivity.  There are many reported cases of people achieving orgasm purely from inflation.

Law of Partner Reassurance:  Anyone who says things like "Don't worry, I won't blow you up too big," or "Just tell me when you're feeling full and I'll stop," is lying.  People invariably change their minds about what qualifies as "too big" once their partner has been inflated too much to have any meaningful say in the matter.

Law of Cosmetic Equivalence:  Compressed gas is a suitable, and in many cases superior, medium for use in cosmetic enhancements.  Breasts filled with helium will be significantly rounder, lighter, and firmer, but will nonetheless be indistinguishable from their natural counterparts even when subjected to the most intimate of scrutiny.  However there is a limit to this effect.  If a woman inflates enough that her breasts take on a latex-like sheen, squeak when rubbed together, or lift her from the ground, then her lover may notice that something is amiss.

Law of Research Ethicality:  The International Ethical Guidelines for Biomedical Research Involving Human Subjects contains a blanket exception for research involving body inflation.  Really, it does.  Look it up.
First Corollary:  There is no corresponding exception in the guidelines governing animal research.  This makes animal testing far more complicated and expensive than testing on humans.  As a result, chemicals that might cause inflation always go straight to human trials.
Second Corollary:  When testing an inflation chemical, it is of utmost important that the test subjects be completely unaware that they are about to be inflated.  Lying to them is strongly encouraged.  The true nature of the experiment should only be revealed once the test subject starts inflating and asks "What's happening to me?"
Third Corollary:  Even better than non-disclosure is an ironic partial disclosure.  For example, a chemical that will fill the subject with a lighter-than-air gas should be pitched as an experimental weight-loss drug or perhaps a mood-altering drug that will "lift your spirits".

Law of Laboratory Staffing:  All research assistants are female, extremely attractive, not very bright, and willing to serve as test subjects for scientists studying inflation.
First Corollary:  Every male scientist has at least one research assistant, whom he will use as a test subject.
Second Corollary:  Female scientists who don't have any research assistants will use themselves as test subjects.