I know at least four people, whom I have to socialize with regularly, who have this annoying habit, or should I say compulsion? of ... how should I put it.... of being insane?

I'm exaggerating mildly. What they do is, when you are having a conversation with them, they don't seem to have the capacity to listen to what you are saying, of making what THEY are saying intelligible to you, and they seem to have very little control over their apparent insanity (e.g. laughing uncontrollably, raising their voices unnecessarily, speaking too quickly or uttering utterly inapproriate things). To me, it seems they are constantly on the verge of completely losing it.

Kinda hard to explain really. I wish my eyes were video cameras and could record what it's like from my perspective, upload it here, for you all to see. Sadly, technology is not quite up to speed, as usual.