In wakeboarding, the forthy dog, is the largest wave that forms during a double-up.
A double up is when the driver of the boat circles and intercescts its own wake at 90 degrees. During that time the waves combine to form larger waves. The largest wave formed during the double up is termed the frothy dog.
When 2 men (as opposed to one) hold their hard dicks together in a hot dog bun, and frot eachother with the hot dog bun. (Frotting meaning 2 men rubbing, humping, or jerking there dicks/genitals together to completion)
Boyfriend one: “It was really funny when you put your hard dick in that hot dog bun”
Boyfriend 2: “yeah we should put both our hard dicks in the hot dog bun”
Boyfriend 1: “yeah that’s a great idea, that would be called frot doging”