[ardubz]

Definitely Bookman, with Denim Vest or Stan The Caddy as close seconds.

I also have to mention this guy even though he's in two episodes. It kills me every time for some reason...

He plays the dump attendant on Kramer's Peterman Reality Bus Tour. They go to dump off the muffin tops and this guy won't let them.

Man: Hey hey hey hey hey. Where do you think you're going?
Kramer: I was going to dump this.
Man: It doesn't look like garbage.
Kramer: Well it's muffin stumps
Man: Where are the muffin tops?
Kramer: This is a garbage dump. Just let me dump it.
Man: Can't do it.
Kramer: Is this a joke?
Man: That's what I'd like to know about it.

He's also the one who refuses to let George get his car out of the lot where it's being used "to turn tricks".