To have an orgasm and release semen
Also see Spurt
keep sucking, im about to unload!!
to use every possible insult you can when verbally lashing someone until they are completely and utterly served and owned. "Unload" refers to someone "unloading" a clip on someone with a gun, releasing all possible ammo into the other person, resulting death (probably.) This is pretty much the same, except verbally.
Person 1: "My girlfriend thought it would be cool to ask another guy to Prom, so I unloaded on her in front of everyone at lunch. I feel much better."
Person 2: "Wow...dude....you rocked her....I didn't know you had that much hate inside you...."
To empty your sack, to explode, to empty your sperm ducts, the male orgasm.
Hey Gaff, you've got a big smile on your face - did you unload ?
Man, I ate a bunch of pancakes & now I have to unload
To urinate. The term is regularly used in contexts when there's no toilet in sight.
Stop the car. I've had too much to drink and now I have to unload.
To sell off stolen merchandise.
Manny: Hey I just whacked this fucker out for about 15 grand in diamonds, do you know somewhere I can unload these?
Larry: Yeah, call up Lenny the Jeweler. He'll give you the best price for it.