Why are people so judgmental?

Why are people so judgmental? I mean when I was at comic-con on sunday I wanted to get furry ears, (either wolf ears or cat ears but wolf ears more) but my sister was saying “Wow. You’re going to be one of those creepy men when you grow up” So…I didn’t buy them since my damn sister made me feel bad about myself with her opinion or judgment on me…But I did buy my wolf tail that I wanted! But again why do people judge on something they don’t like? Or maybe just in general? (I’m not sure the Comic-con thing was really judging….was it?)