First used by Jon Stewart of The Daily Show when signifying the fact that Al Roker of The Today Show was the only person to enunciate the Icelandic volcano Eyjafjjoell more correctly than his peers. The phrase has also recently become somewhat interchangeable with OH SNAP, particularly in cases of giving recognition to funny insults.
see also: OH SNAP
John: BOOM ROKER!
Gus: Hey my sister is dropping by tomorrow is that allright with you guys if she stays overnight?
Andy: That's weird she told me tonight. Oh wait.
Steve: BOOM ROKER!