To have an orgasm and release semen

Also see Spurt, Cum

when you're hungover as shit after a spending a night drunk as a skunk

To empty your sack, to explode, to empty your sperm ducts, the male orgasm.

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.

To take a big shit.

To urinate. The term is regularly used in contexts when there's no toilet in sight.

To sell off stolen merchandise.