I thought it would be cool to start a list of characters who are their own worst enemies. What I mean is people who were always doing stupid things that not only underminded themselves, but sometimes also the people around them!
And here are my picks:
Gilligan--A friend of mine suggested that if the others killed him, they would have gotten off that island in the show's first season!
Lucy Ricardo--She was always doing lame-brained scemes to meet a celebrity, or be a part of the show. These scemes almost always backfired on her!

Michael Scott - The Office (US)

Maybe Urkel, I remember him getting into a lot of jams with Carl. Much in the same manner as Balki and Cousin Larry on Perfect Strangers.

jr ewing he was always trying to pull something and somehow sooner or later it always backfired on him