So this is super classy. My awesome ex got a girl pregnant in our first 2 months of college, he found out and fainted, and she "lost" the baby by downing bottles of Vitamin C.
Anyways, started dating this winner a few weeks later and it ended multiple times, but the last time was because he was cheating on me and getting back together with his ex. (Apparently I was the "other woman", so he said I really WASN'T getting cheated on if I thought about it.)
I wasn't thrilled and we had a history of being awful to each other (low self esteem and alcohol being mixed wasn't awesome). He was no angel either, so a few months later I was bored and decided to ruin his life for a little bit.
Background - He got the girl pregnant during a 4-some (3 guys 1 girl), so it's not like those two had a deep connection.
Soooo, 3 months after the poisonous douche was removed from my life, I casually struck up a conversation with the girl he got pregnant earlier in the school year. I was bored and told her that we were like, totally twins, because he got me pregnant too (nope), but SHHH he doesn't know. She takes the bait and freaks out and offers to break the news to him gently. After pretending to protest, saying "I don't want to ruin his life, I'll just raise it on my own..."...I "reluctantly" agreed to let her inform him.
About 15 minutes later, an unknown number on my phone starts blowing up my phone, I grab a beer, watch Hulu on my laptop and relax while I let my phone go for a few hours.
At about 2 am, I finally picked up. I spent about 10 minutes pretending to not know what he was talking about, spent 20 minutes not confirming anything, and telling him "not to worry about it, it's not your business". He decides to start denying it's his.
"Okay there's NOOOOOOO way it's mine, you've TOTALLY had sex with other guys since we broke up."
I take a breath, and I go, "You're right. I've slept with someone since we broke up. You want to know how I KNOW this baby is YOURS?"
"How."
"You're the only guy I've EVER slept with that couldn't GET IT UP with a condom on. Therefore, YOURS."
He burst into tears (he had about 10 years more of school) and swore he'd do everything in his power to force me to have an abortion, blah blah blah. I told him he could tell his lovely 16 year old gf (we were 18), or I would.
I let it ride for about 3 weeks before I magically lost the "baby".
Super shitty, but waging psychological warfare was how our awful relationship worked. Maybe he stopped cheating on people after that. ;)