Back when I was a kid, everyone played cards. Texas Hold 'Em, Magic: the Gathering, Pokémon, you name it. Then came Munchkin. Within two weeks, we'd gone from curious about a card game that apparently took the mickey out of every single fantasy novel, RPG and tabletop game in existence, to completely hooked. We played loads, and I personally owned a copy of the great-but-less-fantastical Munchkin Fu within the year.
Fast-forward a good seven or eight years, and I'm about to go on holiday. We're taking a few things to do, and Munchkin had popped back up in my Amazon surfing habits recently. I went for it, and could not stop talking about the thing until it arrived. At which point, I kept on talking about it.
Munchkin is simple - two decks, Door and Treasure. A levelling system that for once makes sense, and an element of sabotage that will have you cursing the names of your friends as you laugh and plot your own methods of taking them down a peg. From bizarre monsters to hilariously cliché weaponry and items, it's a good laugh and I strongly recommend a large group of players for the ideal amount of laughter and curses.
Do make sure you take care of the deck though - the die is fairly robust (and well designed, the one is a Munchkin face), but the cards are fickle, so either use protectors or don't chuck it in your school/work bag without a thought for the horrible bent format you'll retrieve them in.
If you're tired of the endless depth of RPGs, then by all means support Steve Jackson and pals and show the world that fantasy roleplaying games don't have to be a serious and self-important as most people would have you believe. A giggle, and a triumph.