I know for sure that you can build "some" immunity to pepper sprays and stun guns. They hit you with both in the academy so you will be less suprised by the effects. The instructor would shoot the spray in his mouth and hold the stun gun(while discharging) to his throat at the same time
and just keep on teaching!
Then he got out the "tazer"
Different outcome there. Everyone hit the floor, standing up is just not an option. Everyone would hold hands and he would attach one lead to each person at the end of the human chain socks. Hit that trigger for just a second and ...
OC just can't do what a tazer can for sure, and a tazer won't blow back in your face