Extremely, entirely, absolutely. The correct spelling of the word as it is used, especially in the Deep South, is plumb, not plum.

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

an extraordinarily large set of nuts that resemble two plums swaying gingerly in a latex glove.

To have casual sex with a girl.

derrived from how many pornos involve plumbers.

to shove your tool into a girls dirty snatch

A simpleton, dunce or idiot. Sometimes used in London.