In all honesty, I know it sounds weird, but when you watch "Seinfeld" for real, it's not really a cynical show, it's more surreal/bizarro/hysterical comedy. It's really light-hearted observation humor in early seasons (in which the dialogue was the most funniest in my opinion) though much better, pushing the envelop. I wouldn't go as far as to call it cynical.
"Friends" (which I can't stand) is way more cynical, orthodox and Calvinist. Well there are two types of Calvinist -- arrogant and very cynical (still arrogant). But then again "Friends" is partially drama anyway.
No I don't think a comedy could do cynicism well. It wouldn't be funny. I don't think pure comedy and cynicism go together. People watch a comedy for laughter not to be depressed.