Similar to a donkey punch, a Cash Smash is the act of doing a girl (or guy) doggy style, while playing a Johnny Cash song on guitar, and then right at the moment of climax you smash the guitar over her/his head.
"At the moment of climax, I performed a Cash Smash. I raised my guitar up high over my head, bringing it down swiftly as I blew all over her back, while wood splintered all over the place and the strings kissed her forehead after it went through the guitar."
by Destroyer7795 November 15, 2007