Mandolin
From Memory Alpha, the free Star Trek reference
The mandolin is a small, stringed guitar-like instrument.
When Q abducted the senior staff of the USS Enterprise-D in 2367 and displaced them into a Sherwood Forest-like environment, Geordi La Forge played the role of Alan-a-Dale.
Completely in character, he tried to play the mandolin, very much to the dislike of Worf, who smashed the instrument into bits and pieces, although he did apologize. (TNG: "Qpid")
