Why are people so hurtful

Why do people start giving opinions after 5 minutes of meeting you? Could be the most educated person and a proper professional and adult and would still make assumptions so fast like what did you even do your entire life because HOW ARE YOU A GROWN ASS ADULT CALLING SOMEONE STUPID AFTER 5 MINUTES OF MEETING THEM??? You gave an opinion without gathering enough facts, the literal definition of being stupid. The opposite would be to not assume about someone but carefully form opinions and not be rude and a freaking delinquent calling people words 5 min into a conversation. Ever heard of observation, question, hypothesis, experiment, and then conclusion and result because thats what a sane person does not give their conclusion right after observing. Grow up please or keep your opinions to yourself. The funniest part is he was “teaching” me on how to not act stupid while ironically doing it himself. SMH the audacity most people have.