coined from the hit movie "Mean Girls" by the excellent actress Rachel McAdams. It can mean many things, either friendly or non. Mostly used as a greeting, or as a burn, bitch.
Jeanean: "Hey Kylie!"
Kylie: "Boo you whore! what are you up to girl?"
Geneva: "I'm so upset! My boyfriend David broke up with me!"
Olivia: "Boo, you whore-- get over it!"
Barbie Barbara: "Damn, I'm hot in my A&F jeans."
Emo Emily: "Boo, you fucking whore! Get over yourself, cake face!"
Kylie: "Boo you whore! what are you up to girl?"
Geneva: "I'm so upset! My boyfriend David broke up with me!"
Olivia: "Boo, you whore-- get over it!"
Barbie Barbara: "Damn, I'm hot in my A&F jeans."
Emo Emily: "Boo, you fucking whore! Get over yourself, cake face!"
by Sophie_Fatale December 9, 2008
Get the boo you whoremug. it is bigger than a boo yaa, which is slang for a 12 gauge detonation. this is like both barrels or say a piano falls on yer head or say a large rifle caliber goes off (.50 bmg or .700 action express) and shoots a cashier at stop n go and rips him in half. if a boo yaa its usually boo yaa boo yaa but boo-yaka-shaw is only used once.
you got a 12 gauge loaded with slugs and this punk starts talkin wak and every time you shoot him you tear off a shoulder and arm or blow offa leg. thats boo-yaka-shaw
by who dat November 7, 2004
Get the boo-yaka-shawmug. by Alex Wander February 25, 2008
Get the Spiggity Boggity Boomug. by iloveucookie August 16, 2015
Get the damn boo savagemug. 
by Ethan! The boo-yah-yah-iest of them all! November 11, 2008
Get the Boo-yah-yahmug. "Jeees boo, Jeees" (j-eheheh-s b-oo, j-eheheh-s) is said when a white girl/ wannabe white girl strongly agrees with something.
by sdbg'a December 12, 2013
Get the Jeees boo, jeeesmug.