When you mix laxatives and aphrodisiacs to induce a shit storm in which you will stroke your johnson while on the shitter. Bucklesloshing is specifically only when you ejaculate during this event.
Ayden: "Bro I mixed the honey packet with the dookie pills and I've never nutted harder."
Joey: "What the fuck are you talking about."
Ayden: "It's called Bucklesloshing buddy, lock in."