big fat peepee. Ok time to analyze.
Big: Substantial in size
Fat: Plump, well filled out
PeePee: Male reproductive organ (baby making machine part 1)
Put'em together and you get a sizable well filled out male reproductive organ. Damn if you needed the urban dic for this I suggest you finish elementary school.

Also used as an insult many times adding "head" to the end.
Oh shit. I was at the stalls the other day and being the stupid gay fuck that I am I looked over at the guy next to me and I noticed that he had a big fat peepee! Man, girls would get pregnant just looking at that thing!

In an insult:
Hey what kind of big fat peepee head are you? Only a big fat peepee pushes other kids off the swings!
by Benji June 25, 2004
Get the big fat peepee mug.
From the Greek phrase "peepeeus biggus fattus."
Classic use; "Socrates you can just eat my peepeeus biggus fattus."

Modern use; "Hey you get away before I whip out my big fat peepee and slap you."
by Robert June 30, 2004
Get the Big Fat PeePee mug.