Another one here who got told by an ex-boyfriend that he "must have got his genital warts from me", because "I had had more sexual partners than him". The facts that:
a) He had spent 4 months in the UK (and me staying in New Zealand), he did not have them before, and came back with them...
b) I had never had had them myself, and...
c) I never subsequently suffered from them after that...
...were not enough to make him change his story.
Fortunately, I dumped him before he could pass them on to me. I bet he still tells his new girlfriends I gave them to him.
Oh, and another good one from an ex of mine:
Me: "who were you talking to on the phone? Was it your ex?"
Him: "No, it was a guy from work"
Unfortunately for him, he failed to notice he had been talking to her with the hands-free switched on.