How rude (but how typical)

I work in a field in which many of my co-workers lean to the left politically.  Doesn't really matter, we don't generally talk about politics anyway, and we tend to get along quite well.

I have noticed, however, that there seems to be a tendency on the left to make rude comments about conservatives as though there weren't any in the room to be insulted.  Either that or it is assumed that you deserve to be insulted so your feelings don't matter.  I don't know which is true or if there is another explanation, but on more than one occasion someone has felt the need to make a slighting comment about conservatives in general in the middle of an otherwise completely apolitical discussion. 

Today, getting ready for a class that I am taking which is being held at a local public high school, mention was made of the Republican Party meeting happening at the other end of the school, down by the main doors.  The RP rented the school premises for their meeting, as they do every month.  One teacher mentioned that it was "Republicans" having their meeting (emphasis on the R word) and another of the teachers present said "It was a little scary walking in".

Seriously?  This is the kind of joke that is acceptable in polite company?  I have to think that she assumed that none of us were Republicans who would be offended.  I can't remember when I have heard it the other way around but maybe I just didn't notice because of my own biases.  I do know that I remember this type of comment at least four other times and I am racking my brain to think of a time when a conservative made some snide comment about "Democrats" while in a group of teachers.