'OMG WTF BBQ' is basically a way of making fun of someone who always uses extraneous acronyms while chatting/talking. Examples include omg, wtf, lol, lmao, cba, tbh, ftw, ftl, etc.
OMG WTF BBQ was made for people to use when they can't stand the acronyms anymore. It's generally understood that once you are BBQ'ed, you must end the acronym talk and speak actual English.
Person 1: "omg, wtf... cba, tbh..."
Person 2: "OMG WTF BBQ!"