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1.
Used as an exclamation when something incredibly spectacular happens. It can also be used to describe a clutch performance or an otherwise impressive feat.
As his teammate clinches a victory, Jake exclaims “Boom Baby!!”

When something 'extra' special happens, just add "Kaboom" for emphasis...

"Boom Baby, Kaboom!!!!"
by Rsquared November 23, 2007
 
2.
It is the first two words that come to your mind when you hear the persons name or see them and you think he/she is a fucking piece of shit douche.
Guy 1: "Barber wants to come over and get baked."
Guy 2: "BOOM BABY!!!!"
by twilth November 08, 2009