Drow Lesbian Stripper Ninja
How is this bad? Other then the ninja part
http://www.boardgamegeek.com/wiki/page/family%3A4458One-dimensional, everything about their character involves sex, usually played by a male gamer, hits on the DM's NPCs and other PCs to make everyone at the table feel awkward, etc.
It's not the character concept so much as the player's juvenile antics. There was once a Goblins webcomic strip that addressed this very issue.
DLSN, while in the middle of a dungeon raid: "Want to see my boobs?"
Other PC, in character: "Now is not the time! Seriously, it's as though you were plucked from the mind of a horny teenage male's ideas on women!"
And now another bad character concept:
17th level Githyanki Cleric (Brownie points to whoever can find out why this is bad!)