Refers to the space in pants/jeans for the male genitalia. Think boxers vs. briefs, or tight pants vs. loose jeans.
I like to have plenty of space in the trunk for the junk. It's more comfortable.

My pants are too tight, there's no space in the trunk for the junk!
by John Preston June 27, 2010
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Marijuana that is horrid. Mostly shake, stems and seeds, doesn't get you high, and doesn't last. Complete garbage.
I'm good on that mexican trunk junk.
by SmokeyBluntRoach November 15, 2014
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