I kinda think similarly to MrRazot. Though I won't deny the fact that I do judge people quite a bit, but I'm aware enough to not take my judgments seriously and don't treat people any different unless they seriously do something to rub me the wrong way. I will poke fun at how someone appears (not real physical appearance, normally. That's very rare for me. I'm thinking more of online contact.), yet still have an honest conversation with them as I would anyone else. Basically, I take note of a goofy thing about someone, laugh at it to myself, but don't let it get to my head.
Now, as for perverts... now, it's normal for most people to have a sexual side. It's all part of nature. Sexual attraction is certainly not perversion or sexism. The word "pervert" and its different forms seem to be stretched and thrown about to the point where it just means "someone who enjoys sexual things".
However. I once dated someone who would touch me in "sensitive" places without my permission, even continuing to do so after I told them to stop several times. After we broke up, they would only talk to me about what I've done in bed, and when I would try to have a clean roleplay with them, they would turn it into blatant sex roleplays.
This, in my eyes, describes a pervert. Perverts are obsessed with sex, and ignore many or all of the boundaries of other people. These are the type of people I really, really dislike.
However, if the pervert is young (such as my example, at that time), they are likely dealing with the goofy stage of growing up, where their hormones are going full blast. This will most likely even out as they get older, and they will stop being obnoxious and learn self control. But many, many people just never grow out of it.