I don't think there is such a thing as reality for humans. There is only everyone's realities adding up. When people say: "you shouldn't judge", it might be a nice thought but an impossible one to achieve (most of the time anyway) since we always interpret things. It is our way to gain experience and gage situations.
So following that chain of thoughts, I think we never really know who someone is. Our understanding is filtered through our experiences. No one is seen and known (in people's heads) as who they really are, they are only interpretations of them.
So I think when you call someone an asshole, unless you are intentionally being malicious, responsibilities belong to both parties.
It is a commendable goal to try to judge less and if everyone tried, everyone would be better off for sure. However, it is also everyone's responsibility to treat others appropriately and not take it out on others or at least warn them that something is going on in their lives that affects their behaviours and that it's got nothing to do with them per se. If not, how is one supposed to know?
It would be awesome that if someone told me they don't like me it wouldn't bother me at all, but that's not the case. Honestly, I'd rather be liked by all (and throw in being awfully rich while we're at it). Of course it'll annoy me more or less depending who it comes from but anyway, since it's the same for pretty much everyone (people who say they really don't care about what anyone thinks of them are in my experience lying) I feel that everyone has to be responsible for what they let on about themselves and how they make other people feel.
We have very dysfunctional ways of interacting with other people that sometimes make people miserable and while I don't want to add to that load, I won't make myself miserable to tolerate all behaviours around me. I can try to understand them as much as possible, but it rarely excuses them when the behaviour is making people unhappy when it could have been avoided.
Of course we all should try to judge less and we all should try to treat others decently and although I am certainly not saying anything original (if anything it's cliché) but it is still astounding how very little effort people are willing to make on that department. So I am willing to make some efforts, but I'm not willing to find excuses for people anymore.
If I say you are an asshole, it might not be the most appropriate or nice thing to say but chances are you acted like one towards me. I am always willing to review my opinion because everyone has their bad days, but if you keep being an asshole to me, I refuse to feel like I shouldn't think of you as one.
So basically, I'm going to take the responsibility for calling you an asshole. But you have to take the responsibility for being one