So, I only roll up my pants on the drive side, but it turns out that there's a li'l protrusion at the base of my non-driveside crank, and today it caught my jeans' cuff just as effectively as the chain would. So, going at about 25 through an intersection, all of the sudden I went into a surprise skid, with 100% of the stress on one very unwilling ankle. 20 feet or painful screaming skidding. When my jeans ripped at the knee from the stress, I though it was the sound of my body breaking.
The setup that caused it is this, except it was the non-drive side, and I have clips and straps now.
Anyway, if y'all run BMX cranks, I really recommend rolling up both legs. I'm here with a bag of ice and a beer, when I wanted to be pedicabbing.