Dancing move used mostly while dancing to fast electronic music, where the dancer slightly leans in and pretends he pulls the activating cord of a chainsaw (the dance move obviously refers to old, gas-activated chainsaws). Also known as "The Lawnmower" for obvious reasons. A perfect example can be found here:
this act is done when a man buttfucking a girl gets tired, so he removes his johnson and begins shoving his arm in ant out of her asshole so it looks like a chainsaw
Nah bitch, I'm too tired to keep fuckin' yo fat booty, Imma give you tha chainsaw!