The act of forcefully farting (you can be clothed or naked) with your ass inches from someone's face (or grill). You get extra credit if they feel the wind or ass spray on their beak. The terminology derives from the fact that you are basting their grill in your own unique brand of stink.
Damn! Did you see that!? Eli just got grill basted by a 325-pound woman!! That fool is gonna smell like a mix of ho-hos, chocodiles and ass for the rest of the day. What a chump.