the low pitch echoing sound which is heard when one expels gas while sitting firmly on the toilet. Most commonly found when the air between blast of fecal matter is released while having diarrhea.
I walked into that bathroom and the dude in the last stall was playing the porcelain trumpet like a pro.
When one person validates another's virgin anus with some foreign object, such as a glass bottle, baseball bat or a set of num-chucks. Due to the fragility of the virgin ass, glass is used to repesent it's delicate nature.