Any "doggy-style" penetrative sex, anal or vaginal (preferably anal), that is performed on the receiver as they are bent over the toilet vomitting. The effect is enhanced if it is a roaring vomit, and the pelvic thrusts are timed to coincide with each regurgitative evacuation.
Last night, my wife got very drunk and demanded that I make love to her. In the course of doing so, she became very ill, and interrupted our intercourse so she could throw-up. As I was incredibly worked up at this point, I marched right into the bathroom and performed the previosly elusive woodchipper on her as she went about her business. However, it was only vaginal.