Meaning the show/event has ended, this comes from the announcements that used to be made at the end of musician Elvis's concerts in order to get fans to leave the arena. Now we use this term anytime an event has ended.
Cindy: OHHHH, YEAHHH, OUUHHH, FUCK ME, CUM ON ME BABY!!!
Jacob (cums): Elvis has left the building (collapses on the floor).