We all judge people. We also are prejudice. It is built in to the very fabric of society, from the way we teach our children to view strangers, to the salesman that comes knocking, to the way we scan a club or social for someone to talk too, etc.
I interviewed many people for jobs. I may have their resume, but much of it comes down to a 10 minute discussion, where I need to evaluate everything from how they talk, dress, personality, etc. I need to judge them, and perhaps even use "prejudice", meaning "pre judging" based on many things, most based on stereotypes.
Some call it a "gut feeling" of why you buy from one salesman compared to another, even though the product is the same. Or why you hire one person over another. It certainly can not be because you discussed in detail every possible item to actually know a person. So you go on preconceived notions, stereotypes, experience, etc. I may not know anything about the 18 year old guy walking in with 23 piercing on his face or the complete "sleeves" inked on his arms, wearing shorts and a t-shirt. But I'm not going to hire him regardless of the 10 minutes we spent chatting.
We judge people all the time. Without knowing anything about the person. We have preconceived notions about three dudes hanging out on the street corner, the very fat slob mother who smacks her child in walmart. The list is endless.
We also are programmed (clan mentality) to group ourselves into groups we ourselves can relate. That mere fact goes a long way in judging others. I see it with everything from biker groups, to unions.
Judging people, usually means not agreeing with something that person has done, perhaps even condemning their actions. I judge my kids actions, my friends (or ex-friend in the case of one who had a problem with young girls) and about anybody else.
Judging others, and being judged, plays into your id, ego, and super ego. It can also play a part of sympathy, empathy, and many other intertwined emotions.
I think many "think" they do not judge, or hold preconceived notions. But I think, and lets call it my judgement on them, is that they are wrong.
With that said, I think many confuse judging, or prejudice, and confuse that with bigotry, racism, and actions that deny rights or liberties.
Show me person who claims to be free of prejudices, or has never judged another, and my judgement of them, would be that they are not being truthful with themselves. :-D