Well, I'm exaggerating to say that one might assume that everyone also hates them, but I think it's a pretty common form of projection to think "I hate X, so other people will probably hate it too".

I can believe that as a starting point where there simply isn't any other information (like it's similar but opposite to the situation where people introduce their friends to friends). However, once you've seen them interact with others, it means making a number of misinterpretations about friends' visible reactions, plus misunderstanding what they like and don't like in people and so on. I think all that is rather less likely.

It's one thing to think that someone "lacks social skills", it's another thing to assume that they'd therefore be glad of my assistance and tutelage...

I agree. Because I've summarised, I've probably made the original claim look worse than it actually was; although I feel that there was a certain element of that in there.

I'd possibly go further and say that there might well be people who find the person annoying but nevertheless like them.

Yes, I can identify with that. I've heard other people make that sort of statement as well.