First I call my girlfriend. I convince her to leave me a voicemail telling me she's dumping me, hates my guts, and I then have her proceed to roast me. I conveniently leave my phone lying around, so when my future self comes looking for me, she hears my phone buzz with the voicemail. She'll check the voicemail and start crying. If that isn't enough to catch her off guard and beat her, I'll tell her I ran over my girlfriend's dog, and that's why she's so upset. "But it's no biggie!" I lie. It's a biggie. My future self knows it's a biggie. She'll be destroyed. Easy win.
Alternate answer: I wait until I know my future self is about to arrive, and I pick up my phone. I call work and tell them I can't make it in for the next few weeks, and proceed to get yelled at. When they ask why, I tell them I am suffering from extreme diarrhea and can't move from the toilet. When I'm done with that, I call my dad. I tell him that I'm gay, and that I've been masturbating since middle school. When he hangs up on me abruptly, I call my girlfriend. I tell her what my potty schedule has been like for the past few weeks in depth, and the consistency/quantity of my droppings. Afterwards, I call my grandma and I begin to read my favorite erotica to her. By now, my future self has already died of second-hand embarrassment... My biggest weakness. It'd be an easy win if my current self didn't have extreme anxiety.
Alternate Alternate Answer: On the night my future self comes, I'm at my girlfriend's house. When my future self arrives, she checks my girlfriend's room where she thinks I'll still be sleeping, but I'm not. Instead, she finds my girlfriend laying seductively on the bed. "You've kept me waiting long enough," she says promiscuously. My future self won't be able to resist. Right when my future self is about to climax, I bust in and wack that *****, sentencing her to something worse than hell... She didn't even get to finish!!!