Admit it, the hockey player's right: you don't get the joke.
We would have done this joke when it was still cold outside, but both skaters are from Lego Minifigure Series 4, and they just came out last month. Blame Lego.
The ice they're skating on comes from the Winter Village Bakery set, which was the second in the series begun by the Winter Toy Shop.
So, the joke itself. The 1992 movie The Cutting Edge is about a hockey player who's forced to take up figure skating. Being used to hockey skates, which are smooth all along their length, he keeps tripping on the figure skates' "toe picks" - spikes at the very front of the blades used to help with the jumps and whatnot. Hockey skates glide on the toes, figure skates bite into the ice. So anyway, he'd fall over, and she'd make fun of him by declaring "toe pick!"
Additionally, "hollow ground" refers to the way the bottom of skate blades are made: there's a groove on the bottom, so technically each skate has two blades in contact with the ice.