Can take place in a variety of situations - but usually at a party, gala, event, etc. It is when a man is receiving any sort of sexual pleasuring to his penis and right as he is going to blow his load, someone behind him opens the door and startles him, causing him to turn around quickly and shoot his hot cream onto the face of the person who opened the door, aka the "interruptor."
Drew: "Hey man get me a beer from that back room."
As door opens - Steve gets a hot cream to his face.
Steve: "WTF!!! I cannot believe I just became an Indianapolis Interruptor."