Why are these mean student librarians gossiping and laughing at someone who goes to the library every day?

There is a guy who goes to my school, and I see him in the library every time I'm there (which is about twice a week). So, it's fair to say that he's there at least most of the time (when he's not in cl). That fact didn't catch my attention at all; after all, the library is open 24/7 for students. What bothers me is that these extremely mean librarians gossip and giggle (sometimes near him) about how he's in the library all the time. They say things like "(Hahahah) Oh my God, that guy is always here. Sometimes I see him here after midnight. (Laughing Hysterically) Like Oh my God." What is your opinion of this rude behavior?