riding the seam
when a girl rubs herself on the seam of her trousers or jeans to feel sexual arousal.
in a boring maths class
riding the seam
When a woman achieves sexual arousal by wearing tight jeans. This occurs when the seam of the jeans comes into contact with the clitoris and, by pressing one's thighs together, creates a pleasurable sensation that often leads to orgasm.
The guys at work think I'm just working on reports in my cube, but in reality I'm "riding the seam" every time we have a casual day.