A diet based on making a bowel movement shortly after eating a meal to excrete the prior. Thus keeping a person at a consistent weight.
Person 1: Yo' Flossy.
Person 2: Sup?
Person 1: Hey man how do you stay so thin.
Person 2: The one in one out diet, I be shittin' all the time!
by Flossy May 27, 2005
The second most horrible viral video, following one guy one screwdriver. It involves a (so far) anonymous man, who squats down over a jar, sliding it up into his ass, and squeezes it with his anus, causing it to shatter in his rectum. Rather than screaming in pain and calling 911, he just grunts, then begins to pick the shards out by hand as a sizable pool of surprisingly thick blood forms beneath him.. A mass of scar tissue suggests that this was intentional, and he "performs" on a regular basis.
Hey man, check this out. Have you seen "one man one cup" before?
by Professor the third March 14, 2010
A video which shows a dude getting Fucked up his skinny ass by a 15 inch shlong and shows it pulling out of his ass hole dripping cum (watch with caution.)
"dude I just finished watching one guy one horse!!. That horse had a long ass shlong!!!!"
by Thatquietguy15 January 4, 2015
One guy one cup is a man who squats-naked-on a large pickle jar. After milling around a bit, the jar shatters while inside his rectum and he keeps his camera face, not saying a word. While hearing the shards of glass in his rectum grinding about, he starts pulling them out, bleeding massive amounts of blood.
Bro, I just saw one guy one cup and I can't imagine anything more f'd up!!
by Tymont January 3, 2012
sarcastically making fun of an idiots mistake. designed to make them feel like shit and make you feel like a bigger, better person
craig: damn it, i just drove my car into a tree!
josh: smart one, dumb one..
by wharfytime April 29, 2010
A rule made to make it easier to field while holding a drink. The rule states that a fielder may catch the ball with one hand after it has bounced once. It is important to note that only the hand and no other part of the body can be used to assist in the catching of the ball.
"one hand one bounce" - fielder

"you used your chest and your hand" -batsman

"one hand one bounce" fielder
"it was a clean take and no interference therefore I'm out" - batsman.
by Cricket 123 February 23, 2012
The sudden need to pass a bowel movement right after eating a meal.
Steve - "The doormen of my guts hold a one in, one out policy"
Jane - "Why are you calling me to say this?"
Steve - "Could you ask the waiter to bring more paper to the lavatory, they're all out."
by IanContinentia October 19, 2009