1. When you sit on any surface in a Metro rail car or a Metro station. The germs and filth that envelop your rear cause the degenerative disease that is Metro Ass.
2. Getting banged on the Metro. The recommended place for getting Metro Ass is the partition of black glass at the end of each car.
1. "Ali, you cannot get in my bed tonight. You've got Metro Ass."
2. "Man, I got a great piece of Metro Ass last night."