I once went to a convention that featured George Takei and Marc Alaimo. From the get-go George was his usual ebullient self, but Alaimo was quite surly. Very curt with people, and just really didn't seem to want to be there. By the second half of the day though, he got into the swing of things and was having a merry old time of it all. Laughing and joking with George at the signing table, messing around with fans, he just seemed to be having a blast.
The only reason I mention this boring little story is that the actors are people too, and often have an off day (or half) and that you can't really judge them from that one encounter. (Much as it can be crushing for the fan.)
Personally, this is the only time a Trek actor been even remotely rude to fans.
That's not to say some
of them aren't jerks, of course.