But think of it from the Rock Cpl's perspective! Teaching (whatever the current term for GDT is) to a bunch of aircrew who resent being there can't be much fun and certainly isn't what was shown in the recruiting brochure when he decided to become a Rock.
But remember - he's the one with the CS pellets! So you'd be wise not to annoy him.
The worst 'GDT' sessions I recall where those where someone behaved like an ar$e and annoyed the instructor - such as the miserable 10 Sqn navigator who complained about being told to extinguish his pipe on the firing range...
The 'respirator test facility' was like a London pea-souper (younger readers may need to Google that!) on that occasion...
As for calling a rifle a 'gun'...