when riding in a vehicle with a bench seat, with two men on the outside, the person riding in the middle is said to be skiing. This is because they can grasp the outer men's penises similiar to ski poles.
On the way to London last night i had to ski between john and andy
A common nickname for a Polish person (often at college, in the military, or in groups with people with varying ethnicities or backgrounds) due to the prevalance of "ski" at the end of Polish last names. Also used as a convenient shortcut from lengthy, consonant-ridden Polish names.
Wojchiechowski, Grabowski, and Tomaszewski are all just "Ski"