A cry heard often when African American males perform a dunk during basketball. Literally translates to "Shit in your mouth!" Derives from the act of bragging about jumping so high above the defender, if you were to deficate, it would land in their mouth, thus, 'shit in your mouth.'
*Forward breaks free with the ball, takes it downcourt, sees the defender with his arms out wide, forward runs straight at him, jumps with all his might and ululates "SHEEINYAMOUF!!"
by Capeten May 12, 2009