The day (usually April Fool's Day or thereabouts) when all the mountain employees and locals who don't have to work dress up in absurd tourist outfits and imitate all the dumb gaper shit we have to deal with the rest of the year. Usually involves lots of neon clothing, ridiculous stunts, and massive amounts of alcohol.
"It's gaper day! I'm going to wear my dad's 80's onesy."
"I'm going with a camo hunting jacket and jeans and doing the Texas Tuck all day on the greens."