I used to transit thru Tehran regularly with Kuwait Air in their 727 fleet in the early 90s, I never had any problems.
Since we had a lot of American Captains then, most stayed in their seat in the flight deck, and never spoke a word until the door was closed.
Just had to make sure we taxied exactly where they instructed, and never use the taxiways on the military side of the runway.
Always very glad to leave that place . . .