A: The effect of watching an Assassin in a movie/Video Game or real life and becoming unreasonably ecstatic or aroused.
B: Gaining elation or sexual pleasure from the art of killing someone with great skill, stealthily and/or without the victim knowing who it was that killed them.
C: Witnessing an assassination and becoming sexually aroused instead of frightened.
Person A: "Did you SEE how he lured him into the alley and then slit his throat without him seeing a THING?"
Person B: "Yeah dude! I had an Assassingasm! I think I need new pants..."
Boyfriend: -Sneaks into the room with black clothing and a knife and wakes up girlfriend-
Girlfriend: -Recognizes her BF, becomes aroused by his outfit- "You totally just gave me an assassingasm!"