When one finally has sex after an extended period of abstinence. Sexual intercourse is compared to starting an engine that has been sitting for a while and has accumulated excessive carbon deposits in its inner workings.
Blow your tits off: You remember that night at Dooley's pool party on that fine Summer eve? When I did that double jack-knife twist and blew everyone's tits off? You remember that? And then I went down on Chrissy Orlando on the trampoline later that night?
Experiencing something so splendid that it's beyond mind blowing. Something so amazinglyout of this world, it can only be expressed by comparing the subject to having your dick blown....off (in the best way)