Several comedians I've come across seem to share this attribute. Robin Williams and Jonathan Waters immediately come to mind. To a lesser extent Martin Short. They seem almost desperate to get a laugh. It can become overbearing to those watching.
>Politically, Brooks was a liberal—or so people assumed after Blazing Saddles.
Ooof...some of the liberals you see these days (I consider myself liberal) would be outraged at "Blazing Saddles". I re-watched it recently and wasn't sure if the film would survive today.