Aggressively clueless

A pejorative description of anyone who becomes angry or dismissive about a topic they have demonstrated a clear lack of understanding of.

Bob: Gotta take my kid for shots today. Man, she hates those.
Joe: Vaccines are total bullshit.
Bob: Umm... why so?
Joe: You're just poisoning your kids.
Bob: OK. How?
Joe: Use your head dummy! (Storms off)
Steve: That was informative.
Bob: Joe's aggressively clueless and doesn't hide it well.