When I was in college I went over the handlebars twice in one week for no apparent reason. Then I realized that in both crashes I was wearing the same pair of shorts I had recently bought. Turns out when I stood up out of the seat to pedal hard my shorts were just the right length to get caught on my shifter lever. This yanked my handlebars 90 degrees to the side and sent me flying.

I don't wear those shorts anymore.