Why did the guitar player get arrested?

This clever little joke hinges on a classic comedic device: wordplay. The punchline takes advantage of the double meaning of the word "fretting." In the world of music, specifically guitar playing, "frets" are the metal strips embedded in the fingerboard of the instrument. A guitarist "frets" a note by pressing a string down behind one of these strips, which shortens the vibrating length of the string and changes its pitch. It's a fundamental and necessary action for any guitar player to create melodies and chords.

However, outside the musical realm, "fretting" means to worry or be anxious about something. So, when the guitar player is described as "fretting too much," the joke playfully suggests they were arrested not for their musical technique, but for being overly concerned or stressed out. The humor comes from the unexpected switch from a technical musical action to a very human emotional state, creating a silly image of a musician getting into trouble for simply feeling a bit anxious.