The style of music in musicals. They can range from really freakin' annoying to wonderfully witty. They are used to convey an emotion in the character, continue the story of the play, create irony, or jsut about anything the writer wants.
The most un-PC show tune ever was "Springtime for Hitler".
A song on a iPod or MP3 that is there for show. The owner skips the song when using their player, but keeps it anyway to impress others and show off their musical knowledge.
Kyle (looking at iTouch): You like Linkin Park too? I have an extra ticket to their concert, wanna come with?
Christy: You don't listen to Linkin Park.
Sara: Yeah those songs are all just show tunes.
A symptom or sign that a male friend of your is not hetero.
"Dude, when they broke out in showtunes and started dancing around, I knew it was time to leave."
to imply that a male may not be heterosexual.
That guy is so show tunes.