Harvest Moon: Give people enough things and you can get them to do whatever you want.
Fable 2: Condoms dug up from the ground are still usable. As are hats and bottles of dye.
Fable 2: The world is full of gay men, transvestites, and grown-ups still in the care of their mums. And girls that want to sleep with you so long as you're wearing the right coat.
Fable 2: Dogs do not die. Ever.
Fable 2: See Harvest Moon.
Portal: Sweet and fluffy baked desserts topped with icing are illusionary.
Half-Life: Do not, under any circumstances, piss off the G-man.
Half-Life 2: You don't go to Ravenholm anymore.
Team Fortress 2: If you want to be noticed, call for a medic repeatedly.
LoZ TP: Chicken-people do in fact exist. They live in a city in the sky and occasionally dwell in assorted pots.
LoZ MM: The world is going to end in three days unless you play a flute song repeatedly. Also, stay away from mask vendors.
LoZ OoT: Do not, under any circumstances, piss off a chicken.
Pokemon: Forcing small animals into airtight balls in between fights for their life is completely humane and acceptable. In fact, it's encouraged.
Kirby: Eat the flesh of your foes to gain their strength.
Mario: Jump on turtles and consume mushrooms for maximum awesomeness. Also, stay away from walking bombs.
GTA IV: Never give your cousin your phone number.
God of War: Kill. KILL!!!
Oblivion: Beggars are actually posh englishmen in disguise.
Oblivion: Avoid twitchy wood elves.
Obivion: The night sky is apparently red.
LittleBigPlanet: Making mazes out of glass is extremely difficult.
World of Warcraft: You must be a master of your skill and a battleworn veteran before you are worthy enough to wear a farmer's hat.
World of Warcraft: Tauren rogues exist. They are always there, and they are always watching.
Armored Core: In the distant future, mech combat is both a military engagement and a sport.