Just an anecdote which seems relevant to me but other people might be baffled as to its relevance!
When I was teaching, I went out for a meal with my job-share and our classroom assistant. I got on really well with both of them, as I do with most people I meet or work with. They were nice women, but I did sort of realise that I couldn't be totally myself with them - I suspected they'd think I was being pretentious if I did.
We went for a meal at an Italian restaurant where the staff are known for their friendliness (all native Italians). As we were ordering one of the women must have mispronounced a menu item and the lovely young waitress kindly and sweetly 'corrected' her - just by saying it properly - more in the way of helping her really. Well, my colleague was incensed, took huge offence and spent the whole meal going on about how the waitress had patronised her, upset her, looked down on her etc etc. I did my best to calm her down, because I saw it as a friendly and helpful gesture - not a threat to anyone's self-esteem.
I learned that some people can be very insecure if they feel others are more knowledgeable than they are, and it can lead to problems in the relationship. this was confirmed when we later had a rather posh (but lovely) Oxbridge-educated teacher join the school. They took against her simply because of her voice and her obvious deep subject knowledge.
I'm not saying you can't be good friends with people of different educational backgrounds and different intellectual ability - you can, of course. But I've learned to be wary through experiences like this. Some people can be small-minded, unfortunately, and judge you if you seem to be cleverer or better-educated.