I just thought of something. At the local public library there's a big sign by the librarian's desk listing the library rules. One of the rules is
"Do not stare at the librarian."
I don't know why, but that has always struck me as funny. Why would there need to be such a rule? I suspect that librarians endure more grief than we give them credit for.
Anyway, it demonstrates that being stared at is a universally, perhaps instinctively unpleasant - no, unnerving experience. Maybe we feel we're being sized up as prey?