Noun: A guy who always has a harmonica on him. Unlike guitar guy, he does not have the harmonica on him specifically to impress others. He has it on him as a security blanket, to practice wherever he wants, to busk for money, and sometimes to impress others.
“That harmonica guy chose a really annoying instrument”
“This harmonica guy wants to sit in, that cool?”
“HEY HARMONICA GUY! Can you play TIMBER?!”