Similar to the usage of "Burn", Boom Roasted is said after an insult or "dis"s for emphasis. Coined during the Season 5 episode of The Office titled, "Stress Relief".
"Sami, i heard you're so white you got buried in the snow on tuesday and no one noticed....
When you getboom roasted, it is equivalent of getting burned!
So if you say something and some one has a come back someone else can say "Ohhhh Boom Roasted!"
Girl "Can i play with your ball?"
Boy" That's what she saidd!!!"