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1.
O!
An unexpected orgasm.
Sheila had an O! when she awoke to Kevin sucking her nipple.

"I just had an O! when I changed my thong!" Lisa said.
by ThatGirlinRed April 01, 2007
 
2.
O!
An attempt by the Omaha, Nebraska city betterment committee to create a slogan for the city. Unfortunately in their attempts, they didn't realize the sexual connotations that are now associated with it.
slogan-"Buy the Big 'O!'" Originally coined to keep commerce in Omaha businesses. Now means to go downtown and get a prostitute, or in some other way purchase a means of orgasm.
by Calvin Hobbes September 16, 2006
 
3.
O!
This is the replacement for the word LOL which is a very overused word on the internet O! is a more useful word cause that is what you are rely doing when you say LOL
O! that was a funny joke
by MIKEY March 01, 2005