Because they are probably accounted for as the stereotype of people or just find it fun to judge people by what and how they live or do in life. And they could just be using it to try and fit in to a certain crowd of people to be like cool or whatever DUMB purpose it is that they are wanting. And best thing to do is just ignore them ignorant, non-respectful, and pathetic low life scum bags....
Why not? What makes you think judgment is bad? Judgment is why I rarely hire crack addicts to babysit the kids. Judgment is why I wouldn't place my kids in a catholic school (and I was raised catholic). The only kind of judgmentalism I don't like is personal morals on things like sex between adults, and my excluding that IS a judgment itself.
Even animals judge, although for them it's akin to survival "instinct".
Like it or not, we all come up with impressions of others. Sometimes good, somethings not so much. If you saw a bum on the street, would you go up to them and ask for some good stock tips? Why not? You just judged them without knowing them. It's just a mechanism we use to categorize people and without sufficient information, your assumptions can and often are wrong but with age and experience, you can increase the chances of guessing correct.