The term "fifty one fifty" derives from California Welfare & Institutions Code section 5150, the provision that allows for a person to be held in involuntary psychiatric lockdown for up to three days if that person is deemed to be a danger to himself or others. It isnow used as slang for crazy, etc.
He's areal fiftyone fifty. Alt: They hauled him in on a fiftyone fifty.
A girl who from a distance of fifty yards away appears to be hot, but as you continue to approach you realize that many features that you could not previously see cause her to be in fact unattractive.
Alex to Jeff as they walk to class: Dude check out that blonde girl up ahead, I'm gonna get her number.
After they walk past without stopping to talk: Ok nevermind she was just a fifty yard fake out.
This was a phrase said back in the early mid 90s as a game. If someone messed up something that they would normally try to play off or correct they would have to say "Fifty." If someone else said "No Fifty" before the person said "Fifty" you would get to take your hand and swipe it really hard across the back of their neck giving them an Indian Rug burn if you will (one swipe with a lot of pressure to create friction so that it hurts). Another common form is saying the phrase "No take backs". {Used in the Maryland area.. don't know about other areas}
John: Ah dude 2+2 = 5
Bob: No Fifty
John: Crap
Bob swipes hand across the back of John's neck.