Being the sporting chap that I am, I don't usually approve of cheating - especially in my videogames. However there are occasions when exploiting glitches, bugs, or even just typing in cheat codes can enhance the game and simply make it a lot more entertaining. I remember playing GTA on my playstation 2 and turning all the pedestrians into angry sociopaths or, as I like to call them, "Irish". 
 

So tell me guys... what's your favorite cheat?

IDDQD
IDKFA

eel nats

Don't be so racist Sweep. We just like having fun. 
 
Also: 
 
Up Up Down Down Left Right Left Right A B Start 
 
It's universal.

pow in Age of Empires 2 spawned a baby on a tricycle with a shotgun

I just remembered Big Head mode. Can't beat Big Head mode.

Nothing funnier than driving around in a golf cart dodging molotov cocktails thrown by old ladies. I'm talking about Crazy Pedestrians in GTA: Vice City. 

BOYOBOY I cant play GH2 without it.

rosebud !;!;!;!;!;!;!;

cheese steak jimmy's from Age of Empires 2. It gave you 1000 food.

" rosebud !;!;!;!;!;!;!; "

I remember being at the midnight launch of GTA: San Andreas. This eleven year old kid was outside with with his mom and a friend. He kept bitching at his mom and even told her to shut up one time. He just kept talking about what cheat codes he was going to use when he got the game. I just wanted an invisible cheat code, so I could stab the little bastard. I would take out his mom too, so she would no longer reproduce. 
 
I haven't used a cheat code since.

Warcraft III had a couple of good ones, for example: 
 
allyourbasearebelongtous - Instant victory.

E=MC2 Trooper in Age of Empires.

Debug mode on Sonic 1. I found it as a kid, completely by accident while doing the level select code.  
Loved making my own levels in the sky.

My favorite was probably the "BIG CODE" from the original Turok: Dinosaur Hunter which unlocked essentially everything.  All weapons, slow-motion mode, big-head mode, Level Select, unlimited ammo, God Mode, and much more.  I was just a kid and didn't know shit about first person shooters, so although I loved Turok, I could never get anywhere in the game. 
That is until this code.  Then I could just enjoy blowing shit up.

" IDDQD IDKFA "

alt + f4. The best cheat ;) But seriously the crash bandicoot ones were ridiculous

I see your IDDQD and IDKFA. I'll raise you IDSPISPOPD.

ASPIRINE

" cheese steak jimmy's from Age of Empires 2. It gave you 1000 food. "

" @mracoon said:

" cheese steak jimmy's from Age of Empires 2. It gave you 1000 food. "

Goddamn - that's my favourite. It also got me to try cheese on my steak. I've never looked back. "

Konami code because UNICORNS