Singing out loud while listening to music with your headphones on. Whereas the singer gets the benefit of the music, those unfortunate to be standing nearby are subjected to an unaccompanied (and invariably crappy) rendition of the song.
"I wish that guy would turn his iPod off - his a crapella version of Bohemian Rhapsody is killing me"
1. (n) a painful or otherwise uncomfortable bowel movement resulting in audible vocalization of lament or relief. 2. (v) to audibly vocalize lament or relief while performing a bowel movement.
"Wow bro, feel better? That was impressive but you got no shot at 'The Voice' with that a crapella solo..."