My freshman year of college my cofounder and I were arch enemies in the web programming course at school. There was a competition around the final project and we were on opposing teams. I think it was mostly because we were jealous of each other's skills. That summer we both worked on research projects at school and became friends and caught the startup bug. At one point he mentioned that we should start a company together and I off-handedly agreed (I only vaguely remember this part although he's told me about it many times).

We tried various little side projects but never got very far during school. He graduated a year before me and got married and moved to San Francisco. Now that I've graduated and moved to San Francisco too we both live together in the same apartment with his wife, so in a way being cofounders is like being married for us :-)

Now we just have to find more time to hack on our stuff...