Sadly, I haven't really played in too many funny games.
Sad Clown Gamer is Sad.
I've run dozens upon dozens, upon dozens of funny games myself, from outright comedy campaigns to light-hearted action/adventure one-shots. I've never actually been in a comedic RPG campaign as a player, and only a handful of humorous, or purposely funny, game sessions.
Now, that is a key distinction there; I've not been in many that were purposely funny. By this I mean games where the game's default premise, characters, setting and/or genre is comedic.
This is not to say I haven't been in 'serious' games in which we laughed our butts off (Seriously. Right off. There are few things more embarrassing to explain to the arriving paramedics). Gather together a bunch of like-minded friends, and it's bound to happen. Add in a shared love of Anime/Manga comedies, Monty Python, Mel Brooks, The Marx Brothers, The Muppet Show, Red Dwarf and Looney Tunes cartoons, and, well, your butts are as good as gone I'd say.
And yes, I'll admit to a secret, sinful desire to seeing the women in the group nearly blow milk from their noses. It's how I know I've arrived as a comedian.
So, the funniest game I was ever in as a player...Clare's Dragon?
Yeah. Probably Clare's Dragon.
Clare's Dragon is an American Manga-style comic book, written by Rob Lansley, and originally published by Radio Comix in their anthology series, 'Mangaphile'. The series artist, Kenichi Lo, is an old, and very good friend of mine. He was part of my oft-mentioned New Jersey group in the latter years of that particular gaming circle.
Ken was integral to my running of Wares Blade, Galaxy Quest, and Ghostbusters.
Ken ran a one shot of Clare's Dragon, based on the comic, in which the players played the key characters:
Clare O'Dowd, a normal, mild mannered gal with a strange knack for getting into the least normal situations imaginable. She is calm, cool, collect...oh who am I kidding? She drives like a Nascar professional late for his third wedding, has a temper that gives literal meaning to 'the fighting Irish', and has a pet dragon the size of a large house cat. More on that in a moment...
Betsy Elderberry is Clare's BFF (besides the dragon of course), and a very powerful elemental wiccan. A miscast spell of Betsy's gave Clare her fire-spewing pet.
Peeta (Last name quite long, and difficult to pronounce), an alien teen currently stuck on a mudball in the unfashionable Western spiral arm of the Milky Way Galaxy. In addition to being stranded a million light years from home, he's become a certain baby dragon's chew toy. He is possibly developing feelings for the beast's owner, and has been forced to go to school with the natives. He is trying to figure out all of the primitive tech.
I had the absolute privilege of playing...
Prix, the baby dragon summoned accidently by Betsy. Prix and Clare have a mental bond, enabling each to know when the other is in trouble, and their friend's general emotional state.
I did not speak as Prix (as Prix can not speak English), but instead made noises inspired by listening to Snoopy's 'voice' in the early Charlie Brown cartoons.
I wish I could remember all the jokes, but it was a situation comedy akin to classic Anime like Urusei Yatsura, Oh My Goddess, and Tenchi Muyo. One of the funniest and most fun games I've ever played in without a doubt.