When a person eats pussy by having his/her head sideways in between both of the woman's thighs on his/her head and chin, and succeeds in making her so excited that she moans in notation just like a harmonica.
"I didn't have to turn on the radio, i just played the harmonica in my girl's panties"
When two homosexuals are docking, and create a leclair- then a third homosexual places his mouth on the leclair and quickly moves it back and forth while blowing. This makes the leclair look like a it is a harmonica being played by a crazy man- complete with semen flying everywhere.
Mike liked Ryan and Sam's leclair so much, that he decided to make it a harmonica. Just like when he volunteered at the old folks home, thanking the elderlies.