In high school there was apparently a small rumor going around that I was dating some guy...that I barely knew, and the most interaction I'd had with him was that he was paired up with me in art class for an assignment.
Thankfully it didn't last long, I denied it since it was not true, some other person was like "wait that guy's in another class of mine, I'll ask him", and then I never heard anything about it again.
I think I heard whispers of another "she's dating this guy" rumor, but in that case it was over someone that I actually did hang out with at times (he was a friend of mine). I heard it as an off-hand comment from somebody else, and I was just like "huh, interesting. Yeah that's not happening though."