I skied from the top of Mt. Apharwat in Kashmir at night under a full moon in Feb 04. That's probably the highest I've ever been ever at slightly over 14,000 feet. Runner-up was probably some barely sub 14er in CO in 1995.
Otherwise, it was December 3rd 2003 in Sayulita Mexico after downing about half a bottle of Radness then making a bong out of the bottle and "testing" it, then once the munchies set in, eating about 1/4 of a batch of brownies made with 1/2 a breadbag worth of pot.
I was pretty much non-functional for 18 hours and haven't touched the yerbage since.
Runner-up was 4/20/94 Pink Floyd Oakland Coliseum.