Someone who misses the net by 15 feet on a breakaway/penalty shot/shoot-out.
Can also refer to missing a target by a very wide margin.
Named after the originator of this move, Lee Stempniak, on a shoot-out miss to lose the game for the Toronto Maple Leafs on February 19, 2009 vs. Columbus BlueJackets.
"He shoots, he Stempniaks"
"What a loser, he just Stempniak'd that shot! "
"Way to go, Stempniak".