Maaaan, skiing is one thing, but surfing is another. If you're going to surf on acid, you better be good at surfing. I'm a decent skiier, good enough to not die on black diamonds (double black diamonds are out of the question though, I'd rather not break my neck kthx) but on acid, I would really only trust myself on a nice, easy slope where I can just take it all in and enjoy myself. Then again, if I were a PRO-fessional (look it up, it's in the book) then skiing down a black diamond would be a most interesting experience on acid.
Also, reading the UD definition of acid while on acid.
Seeing a double rainbow on shrooms.