A rock star gets so into the hardness of the music, that he/she actually destroys instruments. Typically this is smashing a guitar (hence the trope name) on the stage as hard as possible, pounding it to fragments with a few whacks. Some rock bands take it Up to Eleven and set their instruments on fire. And these aren't fictional works trying to make rock seem bad. This is Truth in Television. Although it was a few decades ago, so this is now more played with in fiction than showing up in Real Life bands. Compare Great Balls of Fire, Can-Crushing Cranium, Dramatic Shattering.