Some personal favorites of mine, including a few from science fiction TV:

- A person who is not visible (i.e. is "offscreen") to the people watching the television, will not be visible to the characters on the TV screen either. This is why it is possible for a bad guy to jump out of nowhere and surprise the good guy, even if the good guy is standing in the middle of the Bonneville Salt Flats.

Corrollary: people on television have absolutely no peripheral vision.

- A huge explosion will always travel down a hallway slower than you can run.

- Secret explosive devices designed to be planted by secret agents will have bright blinking lights and often make a loud, annoying repetitive beeping noise after they have been secretly planted.

- If you are a bad guy, the more bullets per second your gun shoots, the less likely you are to hit your target, although you will make a very impressive series of squib explosions in the dirt and walls around the fleeing hero.

- Everyone on TV lives in a house that is usually mostly one single huge room. Many live in remodeled warehouses, or some other place that looks like a sound stage fixed up by a lazy set dresser.

- When two wire-flying kung-fu experts kick the living crap out of each other, it is very rare for even a bruise to form, much less the flying blood, teeth, limbs and eyeballs one would normally expect.

- Space aliens look pretty much like human beings with Silly Putty stuck to some part of their faces, and alien women are always stacked like brick shithouses no matter what their heads look like.

- Anyone exposed to massive radiation will change into something interesting, which I suppose is better than the usual puke-fall-over-and-die response.