Hipsters are people who appropriate bits of other subcultures, without paying their dues in those subcultures. A guy who went to art school supported by wealthy parents and now works in an office designing brand logos, will grow a beard and get sailor tattoos and wear the clothes of a manual worker, and he'll claim this makes him "authentic" - to anyone who'll listen, with the clear implication that he is superior to them in some inexplicable way.

That's why people hate hipsters - what they call irony is actually "being an asshole".