This is a cruel and disgusting yet funny joke to do to a friend. A cup a fart is where you walk up near to the victim. Then you take your hand and cup it over your butthole and fart. Immediately following the fart you take your cupped hand and "throw" the fart about an inch from the persons nose, opening your hand right as it gets there. In doing this it simulates the persons nose being right by your butthole when you fart. The person will usually begin to gag and you will laugh your butt off.
I felt a huge fart cooking up so I walked over near John, cupped my hand over my butt then gave him a nice cup a fart. After the cup a fart John almost threw up because he just inhaled air that seconds before was inside my butthole and near my turds.
by farts are funny March 09, 2010
When you place a cupped hand over your asshole & fart in it, then place cupped hand over an unsuspecting persons face.
Mike will report me to HR if I give him another Cup-A-Fart.
by Anonymous June 05, 2003