My loudest show as an audience member was The Ramones at The Santa Monica Civic Auditorium, a cement bunker of a room. Second was Ray Davies Telecaster when The Kinks played The Fillmore Auditorium (or was it Winterland?) in 1971. SO piercing!
But the biggest scare I had was when I did a long audition (eight hours!) with a band that was forming that same year. I was positioned directly across the room from one of the two guitarists. His Guild Starfire was plugged into a Fender Twin Reverb amp, the latter pointed directly at me from about ten or twelve feet away. We jammed from ten at night until six the next morning, and as I packed up my drums the sound of the guys' voices were drastically muffled-sounding, like a blanket was over their heads. Scared me to death! My hearing eventually returned to normal, but I'm sure there was some permanent damage.