Once I gave a girl a ride home from our high school, she was pretty into me but not really attractive (pretty enough face, reddish-brown hair, but a little heavy). We get to her place, she has work at blockbuster in fifteen and it's on my way, so I offer to wait while she gets ready.
I sit on a couch while she changes in the bedroom, making small talk when somebody knocks at the door. She looks out the peephole and starts to panic because it's her ex outside. He keeps pounding, screaming "Is there some guy in there!?" His cries quickly fade from anger and indignation into a shameless sob "PLEASE TALK TO ME!/I just want to talk" etc
Apparently she just dumped him when I had started talking to her a few days before (not bragging, she wasn't hot)
Meanwhile inside, she is crying, slumps down next to me, her shoulders heaving and covering her face.
I became fully erect.
I can't explain why. I wasn't that attracted to her in general... but I was hard as a fucking steel girder as she cried leaning on my shoulder. I tried to console her, patting her head (I had more XP with dogs then women) and telling her it was alright, when, and I swear to God this is the truth, she stopped, stared at my crotch, and said "What's that?" in a way suggesting she knew just what it was, but wanted to investigate, her hand coming down to squeeze it.
I fucking panicked, there was a dude screaming and crying his love for her just outside the door, and she was reaching for my rock hard cock, which I could feel was starting to make a pre-cum wetspot on my underwear.
So I did the only thing I could think of on such short notice. I said "Nothing there!" and punched my dick. I fucking punched my dick to prove there was 'nothing there', whatever that means.
Weirdest part, she tried to hang out with me again after that. I dodged her calls and didn't see her until 2 weeks later in the hall. Our eyes met and she burst into tears.