Technically, each time the big schlong penetrates the white girl's fanny, it pushes air into the vagina. This pumping and pushing creates a wet sucking noise, resembling a fart. The bigger the dong and the tinier the pussy, the bigger the decibels.
A group of black monsterschlongs who made it their trademark of digging tiny white chicks, decided to name their website after the phenomenon of the dogfart.
Guy 2: We better get out of here.