Only counting those where I was a member of the audience, rather than tech crew or similar:
A heavy metal battle-of-the-bands that I accompanied a uni friend to in the spirit of procrastination over some tedious lab report. It was mostly noise, and therefore guaranteed to send me to sleep. I was woken up in time for the band with the best hair. Better than Laplace transforms.
I also accidentally went to a Blur gig at short notice that I mostly don't remember, so maybe that one too?
Otherwise, I've been to relatively few gigs, and usually because I cared enough to stay awake.