On a more positive note, you might say that you want to do a mask remove and replace drill, followed by an air share drill, both at 10 or 15' down on your first dive together. If he doesn't say something like "cool, I'll do it too", then suggest it. If you really are nervous about his skills, then say so, and ask if he's comfortable doing this sort of drill.
One basic rule I have for insta-buddies is "no surprises". No unannounced, undiscussed changes in the dive plan. No sudden surprises of gas pressure well past the agreed upon turnaround or ascent pressures. No sudden attempts to disappear by fast finning off in a random direction.
A sudden unannounced pulling off of my mask or my reg isn't going to freak me out, but it makes me question your mental state, leading to an immediate abort of the dive.