When two Guys (usually) face eachother (may not be facing eachother due to strategical aspects) and start Pissing on eachother.
There are a few variables determining who wins, some times who ever is the least drenched etc. But in the end, it doesnt matter because everyone has fun.
Two guys walk into a bathroom and use adjacent urinals
Guy 1 turns..
2nd guy turns and fires back.
behold a pee fight
The act of urinating on another person in order to gain friendship or impress them.
...and I turned and I yelled, "Pee fight!" ... and I turned and I peed on him. HRRRNNG NYHRRRR!