Well the Tennesee Twofer is a 2 for 1 situation. You start out in the missionary position, dick goes in the snatch and the balls go up the pooper. That's Step 1.
Now, here's where you get your money's worth. Pull everything out, flip the bitch over, throw your penis up her ass and cram those shit-covered balls up her vagine. That's the twofer, and that's how they roll in Tennesee.
For example, I was in Nashville last week, minding my own business when this ho comes up to me and says "S'up fool? hows about some Twofer action, Tennesee style?". Let me tell ya, I got my $5 worth. Tennesee Twofer stylee.