Just remembered another failure. When I was 27, I'd just broken up with a long term girlfriend (like 8 years) and I hooked up with this girl, who was a raver. Full on giant pants, big sunglasses (at night), shitty music etc. Well the first night, we had sex and the highlight was me getting tangled in her giant ass pants as I took them off. So 2 or 3 days later, we went out again. During this "date", all I could really think of was how I didn't want to be on a date, or be in a relationship, I needed a break from all this kind of shit. I was trying to make the most of the night (I also felt some guilt for already having score the first night we hung out previously.. like I had some "obligation" or something). Anyway, we went back to my place, and I pulled out ye olde marijuana pipe to honestly, calm myself down on the dumb thoughts I was having. I said "hey let's watch this" (put on the movie "the Beach") and promptly fell asleep laying on her lap/ shoulder. Basically just flopped on her. I woke up and she was playing with my hair, like "taking care of me" type things. And she started "making the moves", and I abruptly stood up "yo I gotta take you home". Ultimately, I knew I didn't want to make the same mistake. So I drove her home (literally lived like 3 minute drive from me), she didn't talk to me, nor say goodbye and we never talked again.
This might not be a stupid reason, but I went with the not having sex part.