The worst sunburn I ever incurred was after skiing Crystal in cutoffs in the AM on July 27 1974.
It was turning into some pretty sloppy-gooey stuff by ~11AM, so we drove over to Paradise for a PM boot-pack (in alpine ski boots no less) up the Muir Snowfield to about even with Anvil Rock (a bit over 9K') for a ~4K run down to the parking lot. (Anvil Rock is visible in the picture just above the Paradise Glacier bergschrundt, just to the right of the horn of Little Tahoma, and below bigger overhanging cliff of Gibraltar above Camp Muir.) I've skied the Muir & Paradise Glacier (and other lines within MRNP) many Julys since, but always been with better clothing, boots and sunscreen, and a plan, skinning up with telemark gear rather than the taking shin-bang of alpine boots.
I don't regret that less-planned adventure of my youth, but I was in a world of hurt the next day from sun-poisoning, blisters cracking and bleeding on the backs of my knees, etc.
It's about this time of year I regret not having a glaciated volcano in my current back yard.