This doesn't seem to fully add up. This professor you had a good rapport with won't write you a letter because of an "event" he heard about...and you think this event was somebody told somebody else that you were being condescending at a job where the professor never directly worked with you? And because of this through-the-grapevine talk this professor now doesn't even want to contact you...it just sounds like there is more to this.
Anyways, you need to confront it head on. If you're worried everybody is gonna sink your LORs because of a rumor one guy started, then you should just bring up the situation with the professors you are talking to. Ask them if they talked to your friend. Hell, I would ask that first professor for an explanation about what event he is talking about. "Don't contact me" sounds pretty harsh; "I can't write you a strong letter" would be reasonable for something like this.