How often is it that you are sitting in a game, the rest of the people have said what they're looking to play and you glance over and see that one player that's about to vibrate themselves into another reality. Just CHEWING at the bit to spit out their concept.
Speaking personally, that always fills me with dread.
So with a resigned inward sigh you ask, "So, what are you thinking of making?" Then they lay out this character concept that just totally doesn't fit with the campaign you're looking to run. Maybe they've watched too much anime, maybe they like children's shows about tiny horses, maybe they've had too much redbull. Who knows, but in the end its laying there and they look like they're waiting for everyone to applaud.
Humor is a subjective thing, what you find to be hilarious others might not. Even The Joker admits "you had to be there" jokes never work out because the person by default wasn't there. Its like that with "funny" characters. You might be a huge fan of Rainbow Sparkle Horse Hour but the rest of the table might inwardly groan knowing for the next 4+ hours they're going to have to sit through a running gag and try to treat it seriously.
So try to judge the group you're joining, if they're jolly jokers (thank you Shultz) you might be there with JUST the right character for the game. However if they're wanting to play a serious game Princess Sparklebutt might not be the right character to roll out.