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1.
1%
A segment of the population (and originally the biker population) defined by behavior that is morally incomprehensible to most people. A common (and by some accounts required) 'feat' to earn "%1" designation: To have eaten a woman out while she is on the rag.

Also, refers to the known killer(s) within a biker gang by it's members. Though this is falling into disuse.

1%'s most common meaning is simply "crazy", with the specific connetation of an unknown hidden deeper direction of the one who is 1%.
"No way should you deal with that guy, he's 1%"
by Brendan October 10, 2004
 
2.
1%
A segment of the biker population, comprising about 78.3%, that imagine themselves to be outlaws.
Proud to be 1%!
by timecube June 17, 2004
 
3.
1%
A nickname given to a person who does the following

*Whistles way too much
*Says random annoying things just to get attention
*Constantly tries touching you
*Has weird lame obsessions (EX. Charlie brown/Superman)
*Is super tall (kinda giraffe like)
Carly: Hey Wyat stop being such a 1% its really starting to piss me off!
Wyat: I cant help it! once a 1% always a 1%...I cant change it I was just born like this! Can you tell me what 1% really means?
Carly: Well it means way more then this definition on urbandictionary.com but I wont ever tell you!
Wyat: (starts LOUDLY whistling)
by Parrot Luver January 23, 2011