Masturbation that ends by ejaculating inside a vagina.
"Stacey said we couldn't have sex tonight, but we ran out of lube after 15 minutes so I jacked into her donut"

"I was taking care of my morning wood while my gf slept, but I got too turned on and ended up jacking into her donut"

"I usually jizz on her face but yesterday I gave her a jack in the donut"
by Myfamilyjules July 1, 2019
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