People that had their fifteen minutes of fame but stuck around way past their welcome, poster boys for a forgotten or regretful movement or era, etc.. Basically people that are considered jokes of the industry, but that you still like and/or have respect for. My short list for now includes:
Sylvester Stallone and Arnold Schwarzenegger both (I know they're really mostly A-List, but some of their older stuff is pretty cheesy and laughed at. They were definitely both B-List at some points in their lives)
Jaleel White (Steve Urkel...no joke, I think his physical comedy routine in Family Matters was brilliant, to the same level as Chris Farley or Charlie Chaplin)
can't think of any others right now.
One person who I think absolutely deserves to be on the bottom of any F-List is Kathy Griffin. total annoying hack. She's awful. The fact that she not only knows everybody hates her but also decided to embrace it and make a reality show out of it is deplorable.