When you get a cumshot from a person with two penises
"Damn man that porno ended with a double barrel shot"
This sexual manoeuvre requires one male receiving oral gratification from one (or more) female's. When the male in question ejaculates in the females throat, the female will the close her mouth and squirt out of her nose. Thus causing plenty of spaff to speed out of her nasal cavity, causing the Double Barrel Cum Gun effect that is desired.
Dave: What did you get up to last night then?
Matthew: After I finished I made my missus Double Barrel Cum Gun.
Dave: Oh respect.
It's when your nose is really stuffy and you simultaneously blow air really hard through each nostril, which might be enough to blast snot from both of them at the same time, projecting a scattered tapestry of snot onto whatever you happened to be aiming you face at. It can also be done unintentionally, such as when you sneeze really hard and manage to cover your mouth but it gets diverted to your nose, spraying particles every which way. Regardless it's pretty disgusting so make sure you use a damn tissue next time or if you don't have one sneeze into your sleeve.
"Oh well that's gross. That guy just fired his double barrel SNOTgun at his desk and now there's boogers everywhere."
"I was sitting in class and this guy behind me blasted the back of my head with a double barrel SNOTgun. Guess that explains why my nose is feeling a little stuffy and I feel a cold coming on. ACHOO!"
The act of two sexual partners sitting on a single toilet with one sitting on the other, the top half shitting through the legs of the bottom while they themself drop dookage.
🅱️Ethan: “The poop! Its not coming out!!
Everyone: retard stfu stop double barreling ur boyfriend in the Taco bell restroom
When you shit while having a orgasm.
Eric just got a double barrel shotgun from Megan he said it was such a great blow job, he shit himself when he blew his load!
The act of wanking off two men simultaneously into your face.
Sarah pumped the double barrel shotgun into her face.
When a girl is peeing and you insert your penis into her and you both piss at the same time
Jack: Soo you did something interesting this week?
Steve: Yeah, went shopping and double barrel shotgun Emily