as a verb means to masturbate to climax, complete with orgasm and ejaculation of semen among males.
as a noun means cum, ejaculate, semen.
"Oh, you are porking off
", said to me by younger brother, when I was masturbating and emitting pre-ejaculate (precum) from my glans penis. I was a few months away from my first, true masturbation to orgasm, with a spectacular ejaculation of semen (cum).
"Oh, you have pork off
(but that was precum) on your belly," so my brother said, but that was before I achieved masturbation with orgasm, complete with pork off
, cum, semen.
I heard these two expressions about 1964 from my younger brother as I was entering adolescence and he not far behind. We were engaging in innocent sexual play then.