I did this once (well not once, but for the same boy) after he was telling all his friends that I begged him to sleep with me, and after 2 years he finally bang me, so I would stop bothering him...
I was going after every new potential girlfriend of his and just told them that he's got very ugly big hairy mole on his penis, and showing them a picture from the internet, and that actually we never slept together, because when we undress and I saw it, I just ran from there, but he's so insecure about it, and asked me not to tell people, that we hasn't slept together, but I can't do this to fellow sister, you should know before you go there...
And this piece of crap never found out why nobody wanted to sleep with him...
I was going after every new potential girlfriend of his and just told them that he's got very ugly big hairy mole on his penis, and showing them a picture from the internet, and that actually we never slept together, because when we undress and I saw it, I just ran from there, but he's so insecure about it, and asked me not to tell people, that we hasn't slept together, but I can't do this to fellow sister, you should know before you go there...
And this piece of crap never found out why nobody wanted to sleep with him...