Despite the common meaning at first glance this phrase doesn't use jackin synonymous for stealing, as one might originally think, but in reality, masturbation.

To Jack ina Jag is to masturbate in an upper echelon high speed vehicle to show off presumably newly attended levels of wealth.
"I just got a bag from this court case, I'm finna go jackin ina jag now"

or
"I ain't neva going to jack ina jag with these hours, I need to get my bread up"
by ToxicSandwiches April 6, 2023
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