When I was in high school there was a rumor going around that I pushed a physically handicapped kid who went to a different school out of a moving car, killing him, and that I somehow avoided legal consequences. Just to be clear, absolutely nothing even vaguely like this happened. Fictional event, fictional victim. But one guy in school claimed he totally knew the guy I did this to...and some people believed him and I found myself being treated differently afterwards. I didn't even know the guy who spread the rumor about me, I'm not even sure if I even had a conversation with the guy prior to him spreading this rumor. I only found out because multiple other students (independently of each other) told me he not only told them the story, but claims to have known the (completely fictional) victim. When I confronted him, he was a gigantic pussy and kept backpedaling. I threatened him and bullied him a bit after that.
But my reputation (which was already less than stellar) took a big hit and I was seen as a horrible monster to some, including one teacher who somehow believed this story. But to be fair I do remember one guy who wasn't even a close friend or anything stood up for me when the rumor was brought up, saying the guy who started the rumor was a bullshitter.
The guy who spread the rumor didn't even have any personal motivation for targeting me, again, I didn't even know the guy like that. There's some people who really like spreading rumors and damaging the reputations of others. Like they want to fuck with people but they're low T, high inhib cowards. He probably targeted me because I was an ugly, low trust looking guy and I was high T and low inhib and been in plenty of fights and it was known I stabbed a guy when I was in middle school... so exactly the type of person someone would be willing to believe would do something like what I was accused of doing.