What is Playing The Trombone?
1.
Getting your ass licked and being jerked off at the same time!
An extension of
"At first i was like ... is this gay? but then i sort of liked it & realized that it was a girl licking my ass ... then she jerked me off at the same time as if she was playing the trombone or something?"
2.
Jacking off.
"Playing the trombone originated from an American movie in the 70's. The jock of the movie referred to 'whacking off' as 'playing his trombone'
"I played my trombone like a mad musician right now. The spit valve was pouring like a sucker."
See