i never ride subs, but if i did, i wouldn't hesitate to rub one off if i felt the need.
when i was in college, the local video store had a "back room" with the porn. you had to purchase a key to get in it. i had the key, but i didn't have the money to rent that shit. it was like triple the cost of a regular movie. so i would go in there and wait until nobody else was in there and jerk off to the covers & screen captures of the movies. i would just bust a nut on the floor and then leave. after 3 or 4 times doing that. i walked in one day and was informed by an employee that they had security cameras back there and knew what i was "up to" and took my key away.
i could never show my face in there again . . . . .