When the over excitable seaman preforms oral sex on the rest of the crew when they cross over the tropic of Capricorn or cancer while hiding in the dorade vents of a ship.
Hurry up! Davey from the Navy is manning the BLUE TUBA on the overnight watch tonight. You want to get in line early before the Boston Lockjaw gets tired and stops clenching.
During fellatio, your partner sucks on your meat until it bruises. Turning your “tuba” blue.
Damn dude she suck the soul outta me and now I gotta Blue Tuba.