Probably Richie Aprile. The actor did a magnificent job portraying him as a genuine gangster, but the character was a really annoying little prick.

I also find Paulie Walnuts to be annoying from time to time. The same things with Phill Leotardo, Soprano's sister and uncle junior.

I also don't really like Dr. Melvi's psychiatrist. That guy has that really stereotypical smart-ass facial appearence like he's the one who knows it all. Can't stand it. I would love to give him a punch in the face for it.