When a skier or snowboarder eats it on the slopes and loses all of their gear. If a skier loses his skies, poles, hat, goggles, and anything else, shout "YARD SALE" from the ski lift above him.

A stupid person; it refers to the lack of surface area on an individual's brain. The general thought is that the more surface area (wrinkles, creases, etc.) a brain has, the smarter the person is. Conversely, a person with a smooth brain (no wrinkles) has less surface area and would therefore be stupid.

to fall while skiing or snowboarding and leaving a trail of gear behind them

The evidence or remains of a catatrophic accident or wipeout, in which the victim's belongings are scattered or spread out across a large area (resembling a traditional yard sale).

a bad wipe-out on the ski slopes, your shit's all over the place: one ski over here, a pole over there, hat somewhere else

Snowboarding/Skiing - When you fall hard and leave your hat, goggles, clothes, gloves, poles, etc.. all over the mountain

While playing the sport lacrosse, the act of having your stick hit out of your hands, which triggers every player on the field's yelling out "Yardsale!". It is called this because it is lying on the grass as if you were trying to sell it on your lawn.