I think John would only give you crap if you deserved it. For instance, usually people who talk about him have pretty good things to say. The ones that don't, well you have to look at where they were coming from. I've read quotes from Mick Jagger speaking about how pleasant Paul was and how he could only take so much of John after a while. But then, think about Mick and why John probably felt the need to annoy him. His incessant talking about Marianne Faithful lead John to write And Your Bird Can Sing, his comments about the Beatles not being a great live band lead John to talk about his "f** dancing." So I think basically if you came off as a phony or arrogant or just plain annoying, John would let you have it. I think the stuff with Brian Epstein was more of a power play on John's part and the fact that he was probably uncomfortable with Brian's feelings for him. So anyway, I don't think his nastiness was usually unprovoked. Maybe during the drug years though. But that's understandable.
same as above poster, the scariest thing would be to approach a Beatle just to have them stand there and not talk back. - Deadly silence - i vote George, followed closely by John.Macca and Ringo would make you feel welcome i feel.