Cumpacity
The amount of cum a given person can hold in their mouth (or any given orifice) at one time.
Her mouth has a very good cumpacity. I blew two loads in there!
Cumpacity
The amount of cum in which one can take
She is a slut, her cumpacity level is very high
Maximum Cumpacity
When you have had sex (or jerked off) so many times in one day that you lose the ability to have another orgasm.
Last night they had a Jenna Jamison marathon on pay-per-view porn. I beat off so many times, I reached my maximum cumpacity!