Well-known slang term in sexual subculture of chronic and compulsive masturbators, used both as a verb and a noun. Means achieving the trance-like blissful state reached when riding the edge of cumming for as long as possible, perhaps many minutes or even hours at a time. Also denoting the absence of control, compulsively pursuing that feeling as a avid masturbator. The term has been in frequent use for at least ten years, perhaps emerging from the physical look of one who is "gooning" or "in the goon," which is a self-possessed, glassy eyed stare of stupidity (thus, an oaf). Also known as "bator mush" and "slain in the bate."
There I was, stroking for hours, and I was into the goon so deep that a bomb could have gone off next door, and I would not have noticed.
Whenever we masturbate together, I like to watch him goon on his penis ... he really gets into it.