2. Talking about something you don't know anything about while trying to present the illusion you are educated on the subject.
3. The act of saying absolutely ridiculous shit.
Joe: George Bush was the best president the United States ever had!
Jack: Imma punch you in your dumb face if you don't stop that mouthassjackery.
Vince Offer for the SlapChop:
... This thing, this tuna looks boring. Stop having a boring tuna, stop having a boring life. Add this tuna putting it in like this now you’re going to have a nice, tuna, salad. Look at this you’re gonna have an exciting life now.
TV Viewer: LOL - good ole' Vince ... He is the master of mouthassjackery.