Labels. Putting folks into unnecessary groups, intentions be damned. Recently, I've found that putting people into groups, adding labels, saying "you are part of this collective" seems to be causing much more trouble than good. Whether by race, religion, creed, sexual orientation, or political affiliation, I've seen people's opinions of others do a total 180 just by the single passing comment of something like "Yeah, his boyfriend…"

Just stop applying labels to people. It'll do a world of good. Not overnight, but it'll help.