I've been maced twice in bar fights, but one of those times happened as I was helping a bouncer who was getting fucked up. Stupid cops just hit everybody, even the poor bouncer who was down. Also got hit, accidentally by a girlfriend. She was showing off with her "new toy" as I was driving along and bragging about how I didn't have to worry about her dropping a bank deposit at night when I was out of town. It supposedly was still sealed. She hit me right in my right eye with it and I managed to turn my head and got it in my ear. The earful was way worse than the eye hit.
I don't really think it's that bad, though. I've had worse things hit me. In fact, I fell down a hill and rolled through chest high stinging nettles in Georgia one time. That was a much more severe skin irritant than the three mace hits combined. Nettles burn like hellfire.