Is there anything you can do when a professor discusses some of your personal concerns with other professors potentially mockingly? I am an undergraduate student. Recently, my interest about a particular (difficult) field – somewhere between physics and maths – arose, a field that is only briefly mentioned in some lectures. For that reason I decided to ask the only professor (Professor A) who could know more about it. Professor A also happens to be a professor that is, in polite words, student-unfriendly. I simply asked if he could suggest some books or topics I could read in order to get prepared for a book that had the whole theory of that difficult field I was looking for.

His first reaction was laughter. He said that even he himself has not “touched” this particular field and that no one else in the whole university could. In the meantime, he used several provocative phrases to describe how poorly educated in maths students are for such purposes. It is also known that Professor A generally talks with many students in a bad manner and generally misbehaves. Still, he is a good researcher, and other professors respect him for that (and only that – they know about the misbehaviour).

Anyway, the next thing that happened is that many other professors know about this situation and their behaviour towards me is strange. One of them is a professor I would like to work with (Professor B).
I strongly believe that Professor A said something wrong/different about our conversation.
Right on the day I talked to Professor A, Professor B cancelled (not postponed) a meeting: I went to the meeting and he had already left the building. I sent an e-mail saying I came but did not find him. I also included maybe we could meet another time. The reply contained: “I am sorry, but I heard from other professors that you have already discussed the topics you wanted to discuss with me.”

Well, something’s not right.

I definitely can’t ask Professor B directly: “what did Professor A say to you?”. Is there anything I could do? Before contacting anyone else, can I do anything to verify what they had talked about? Or what else could I do?
I was going to vote to close because you're an undergraduate, but I checked the fine print and I think we're okay here -- this is a situation which could easily occur to a grad student.

If you still want to talk to the guy who canceled your appointment so rudely, I suppose you could visit his announced office hours and try pretending the whole thing didn't happen

However, if you don't mind being patient, the other approach would be to learn from this experience that your department is a gossip den, and be more circumspect in future; and trust that after some weeks or months, the good guys in your department will realize that you are a serious student worthy of helping.  This approach could be called taking the moral high ground and biding your time.