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1.
an exclaimation of your point. a command.
"this will be the best blowjob of your life"

"bitch, it best be."
by sma January 19, 2004
 
2.
1. You had better be.
2. You had better do that.
3. Expression of satisfaction.

Also, simply "best."
Albert: "I am a rocker. I rock out."
Ben: "Best be."

Albert: "I intend to give you five dollars."
Ben: "Best be."

"I win at Scrabble! Best!"

by Jeff Moore March 12, 2003