To have outercourse with the female anatomy found between the hip and ribs, usually referred to as the "tummy". Usually performed by teenaged boys still waiting for their balls to drop, or the "special" older male with little to no experience.
We caught Bernie flank-fucking the shit out of Naomi on Paul's new leather couch, the poor bastard.

Want to flank fuck before I have to work at the gas station?
by Township March 16, 2007
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