Comedians are indeed particularly notorious for their moody and often very unpleasant personalities, versus their public personas. There are probably a few exceptions to the rule (never heard anyone say anything but positive things about Oliver Hardy!), of course.
Both Laurel and Hardy were supposed to be very, very nice. Two of my very favorites.
I think, maybe, we’re talking about stand up comedians as opposed to actors. Of course, Danny Kaye was a performer, not a standup, so go figure.