Searching for a fat girl's vagina to initiate intercouse while layers and layers of blubbery lard get in your way. Thus making a diving maneuver completely necessary.
Guy 1: "Yeah, dude, I totally fucked ____ last night."
Guy 2: "Isn't she like 200 pounds though?"
Guy 1: "Yeah. I was totally muff-diving but it was worth it."
To eat out a pussy with a "muff", which is a jungle of pubic hair. This can sometimes result in embarassing situations in which people tell you that you have a pubic hair or two caught in your teeth. Not reccomended for people with standards.
Larry went muff diving once without the properjungle-cutting equipment and got lost for days.
12 step recovery jargon referring to someone new who talks about how great life is, now that they'resober. Usually meaning that the person is out of touch with reality.
The new guy seems pretty happy for a dude who has no job, no money and no family. He must be on a pink cloud.