Auto-erotic stimulation of the anus while driving a pickup. For a traditional Silfen, the fingernails must be cleaned with the edge of an incisor tooth. Extra style points awarded if performed while stopped in traffic and for simultaneous performance with spouse.
"Don't look, honey, but the odd-looking fellow in the pickup next to us just Silfened."
Auto-erotic stimulation of the anus with one or more fingers while driving a pickup truck. For a traditional, or "urSilfen," the same fingers should then be used to pick crusty boogers out of an extremely hairy nose and the fingernail(s) should be cleaned using an incisor tooth. Extra points for simultaneous perfomance with spouse.
"Don't look, honey, but I'll be gosh-darned if the odd looking fellow behind us in the Chevy isn't Silfening himself."