bikers butt is the overuse of your butt muscles and joints caused (in the majority) of excessive biking
like tennis elbow and/or golfers elbow, bikers butt is a result of an over exertion of a given muscular area
Bikers Butt occurs when one is riding a bicycle in the rain. The back wheel shoots water straight up into the ass region of the biker, causing a soggy, U-shaped wet spot on the seat of the bikers pants. This causes major discomfort when sitting in class or interacting with other individuals in a social setting.
"Dude, why is your butt so wet?"
"Well, I had to get to class fast, so I rode my bike. Unfortunately, it was raining and I got a mad case of Bikers Butt. I had to sit on my wet ass for a 2 hour lab. It fucking sucked!!"