A play on the word "orgasm", it's a feeling of complete and utter happiness, joy, ecstasy, euphoria, delirium, elation, etc. having anything to do with the musical "Rent". Whether it's by: thinking about one of the actors, songs, or scenes; singing/listening to one of the songs; seeing the show. This emotion is usually more powerful than an orgasm to a true Renthead.
I had a huge Rentgasm when Tracie hit that high C in her solo.
Jesse's voice makes me Rentgasm every time he sings/smiles/dances/talks.
"La vie Boheme" is such an awesome song, it makes me Rentgasm every time I listen to it.
I Rentgasm every time I even LOOK at my Rent DVD.