Spy Law: When you run out of Cloak and Dagger, a scout or other friendly will inevitably draw attention to wherever you are hiding.
Medic Law: If you finally charge your uber and are not killed within five seconds, you are an invincible god as long as you don't find somebody to use the uber on.
Medic Law Addendum: You'll go for a full minute without any useful classes showing up.
Medic Law Addendum Postscript: The moment you decide "screw it I'm gonna uber that Engineer" somebody will switch to Soldier and complain that you didn't save it for them.
Turbine Law: Three Engineers will all decide to place their sentries on the ledge in the cooked hallway, right next to each other.
Turbine Law Addendum: They'll never learn that sentries placed there cannot reach demomen who put their backs against the far wall.
Turbine Law Addendum Postscript: They will place their sentries close enough to the edge to be easily sapped anyway.
Dispenser Law: Dispensers are most desparately needed when you don't have 60 seconds to build one.
Dispenser Law Addendum: Engineers will always take the last bit of metal from your dispenser when you need it the most.
Dispenser Law Addendum Postscript: By the time your dispenser makes it to level 3 it's only useful as an easy point for the other team.
Scout Rush Law: Scout rushes only work once. Your team will try them every round anyway.
Spy Teleporter Law: Spies CANNOT resist sapping teleporters. Use this to your advantage to discover spies.
HLXStats Law: When your points are low, you'll only kill people with low points. When your points are high, you will only be killed by newbs who sap 25 points a kill.
TF2 Update Law: All new weapons are overpowered and cheap and must be nurfed, except for the unlocks for your favorite class that are refreshingly balanced and awesome.
Medic Blutsauger Dual Law: He who shoots his blutsauger first shall die whilst reloading.
FIRE FIRE FIRE law: There are four ways to put out a fire: (1) Medigun, (2) Medical Kit, (3) Pyro Airblast, (4) Jarate. None of these will be available if you have less than 50HP.
FIRE FIRE FIRE law Addendum: They will appear just before your killcam.
Spy Killcam Law: If a spy is in a killcam shot, he will be doing something awesome.
Ragdoll Rubbernecker Law: If a ragdoll gets cought in a strage way (foot stuck in a level decoration, arrow through a scout's right arm while doublejumping near a wall) it's good for another 5-6 kills as the gawkers stop to look.
Spray Law: Sprays with funny sayings are worth at least one gawker kill.
Spray Law Addendum: Sprays with hot girls are worth at least two gawker kills.
Spray Law Addendum Addendum: Sprays with the ::awesome:: face are worth three gawker kills.
Spray Law Postscript: "This guy is totally not a spy" works for some reason.
Spray Admin Law: You WILL die 4-5 times while trying to get a spraytrace. For some reason people don't spray bad sprays in spawn rooms or intel rooms, always next to enemy sentry guns.
Spy Cloak Law: If two cloaked spies bump into each other, both will freeze (with their cloak shimmering) hoping that the other guy hasn't noticed.
Sapper Law: If you are the spy, there is always an Engineer nearby to break the sapper. If you are the Engineer, you're always too far away to get there in time. If you're the Dead Engineer, there is never another Engineer available to remove your sapper.