A girl that I had just broken up with tried to get me back by telling me she was pregnant. I made her take a pregnancy test in my presence, which came out negative, but she kept swearing on her life that she had taken four positive tests previously. Couldn't find a way to catch her in her lie until she went to the doctor. I told her to put her doctor on the phone with me after she had been examined so she could explain to me what was going on. To my surprise, she completely complied with my request. She put her doctor on the phone with me, who explained to me that my ex had indeed been pregnant but that it had been too long since the two of us got intimate for it to have been mine. She was at another university far away, partly why I broke up with her. She spent another five minutes on the phone with me trying to phrase it in a way that wasn't explicitly, your girlfriend cheated on you and then tried to blame the resulting pregnancy on you. That was a pretty awkward conversation.