For the most part I don't think they are any different than anyother other group.However, I think there are more dubs who laugh inappropriately when there is nothing funny,
My brother and a few others I know do this and it drives me crazy. They have this stupid smile on their face all the time no matter what they are saying and always chuckling.
We just had a presidential candidate who did this. It wasn't her laugh that people mocked it was like "why the hell are you laughing right now there's nothing funny." For her it was a defensive delay tactic to give a reaction to a question so that her brain had time to come up with a reply. Pseudobulbar affect (PBA) is actually a neurological condition maybe that's what they have?