The act of fucking a girl so hard, from any position, so long as the balls smack the female to the point that there is an unmistake, audible, and loud skin on skin popping sound resembling the sound of a breaching whale's tail smacking the water.
"Dude, I completely whale tailed that girl from the bar last night"
A patch of chest hair that goes across the top from nipple to nipple and tapers off to a point in the middle.
Look at that dude's whale tail! We should've drawn the rest of the whale on his stomach in stead of that big swastika. Oh well, he'll laugh anyway.