When you put peaches in a girl's vagina and either whipped cream or iced cream on a man's penis, then proceed to sixty-nine for a minute, then rotate and kiss each other, forming peaches and cream in each others mouths.
Betty and I had peach melvin for dessert last night.
When an old man goes to a parlour and has his bald head buffed until shiny.
Oh hey George, I just got back from gettin' a peach melvin at Paul's Parlour.
Inasmuch as sex, a peach melvin if you will can also regard the orgasm of a large farm animal. I.E: Horse, Cow, Moose, Teridactyl
Knelly was getting dirty with BIG Betsy and prematurely peach melvined.