When Charlie gets crippled, he plays the sympathy card pretty hard at the strip club with Frank.
Added:

It's Always Sunny in Philadelphia Season 2 Episode 1 Quotes

Dennis, your mother is a dirty, dirty whore.

Frank

Charlie [in a wheelchair and army vet attire]: This costume, the chicks is gonna go crazy all over it.
Frank: Maybe you should let me do all the talking.
Charlie: No, it's like shooting fish in a barrel. So watch and learn.
Stripper: Awww, look at you sweetie, what happened?
Charlie: Viet-goddamn-nam, that's what happened! Go get me a beer, bitch!