This is how Charlie Sheen signs off on some of his tweets. It's short for "You've Been Warned"

It appears to be almost a challenge. He will issue some random command, followed by "ybw". As if to say, follow if you dare or proceed at your own risk.

Like a lot of Sheen's catch phrases, no one really knows what it means. But now, you've been warned...
For example: From an actual Sheen Tweet, "Ignite your warrior. Follow my lead. ybw c"
by texastraveler March 17, 2011
Get the YBW mug.
An acronym made famous by the Tiger-Blood drinking warlock himself, Charlie Sheen. He uses it in most of his tweets, in most cases next to different hashtags (e.g.: #winning #sheenius and so on), and the supposed meaning is either "You'be Been Warned" or, more likely, "You'll Be Winning".
Actual Charlie Sheen tweet:

@charliesheen Charlie Sheen

I am not only the book of Sheen-yuss but also the Book of Face.... yuss. go there now. *link* ybw c #sheenius
by DubluVe March 27, 2011
Get the YBW mug.
"You've been warned" frequently used by Charlie Sheen to end his mad ramblings on twitter.
rumors?
fact?
while feet drag,
the warlock levitates.
away from fools gold,
or towards the actual mine.
ybw
c
by elocin277 March 23, 2011
Get the YBW mug.
You've been warned.

Popularized on Twitter by Charlie Sheen on March 8, 2011.
#Fastball; The Warlock is hungry. Hungry for corporate flesh. Live tonite - 7p PST. "Building the perfect torpedo" my manifesto @ustream ybw
by Johnny Haze March 22, 2011
Get the YBW mug.
1. 'You'll Be Winning'. Deriving from Charlie Sheen's overuse of the word winning, frequently posted throughout his tweets.

2. "You've Been Warned" is what he used to say in his video streams, but was shortened to ybw.
by Zojin March 30, 2011
Get the ybw mug.
You've been warned.
Thus The Warlock spake, and it was good.
ybw
by Choadmonkey April 5, 2011
Get the ybw mug.
Stands for "You're Bi-Winning", an abbreviation used by Charlie Sheen on his twitter almost daily.
Charlie Sheen: I'm not bipolar, I'm bi-winning

Charlie Sheen: Coming to my show? ybw.
by blondemomentx March 16, 2011
Get the ybw mug.