Based on the Green Mountain form of a U-turn, which is when you pull your car past a street, throw it in reverse and back down the street. Then enable your turn signal (because you’re not an Masshole) and pull out going the other direction.
As a sexual act, it’s pretty straight forward. Or straight backward, really. It’s when a girl (preferably of the green mountain variety, because girls from VT are known to be hot AF) walks past a dude. Stops in her tracks, and throws that ass in reverse towards said green mountain boy. Backs it up until she’s right on his Dakin Farm summer sausage. She then proceeds to ride him like a Morgan horse while feeding him Cabot cheddar cheese and/or Ben & Jerry’s. At climax, he shoots his 100% pure maple syrup into her homemade apple pie. She gets up and walks in the opposite direction towards some dope fall foliage.
“Jenny came over last night and gave me a Vermont turn-around. Girls from Burlington are straight up freaks man.”