In internet culture, being 'roasted' is when another member makes a witty comment or comeback upon oneself which is cause for all the preteensbehind the screen to scream "OOOOOOOHHHHHH", postpubescents to nod in amusement and oneself to cringe in utter defeat.
According to dictionary.com, roasted means to heat excessively. Most commonly used when roasting someone you call a "thanksgiving turkey". YOu normally roast turkeys, right??