If he continues using them even after all those negative comments then he's either dumb because he can't see they are annoying and pointless, or he's dumb because he can see they are annoying and pointless but continues to use them merely to annoy.
Either stance is a dumb one to hold.
Still not seeing how this makes him dumb, i.e. intellectually inferior, even if he's receiving criticism from you guys. He's simply being annoying (as perceived by you guys) -- no more and no less. It isn't necessarily a simple-minded decision to not back off despite your complaints. Rude, maybe.