It's a very unusual nickname to be given, largely because of Domi's smile, which features several missing teeth, but it also shows just how great of a teammate Domi is and how much everyone in that room appreciates him.
Domi was a Leaf far before he signed a 1-year, $3M deal this past off-season as we all know he grew up in the Leafs dressing room, hanging around his dad and fan favourite, Tie Domi. While he didn't get off to the greatest start in the blue and white, Domi has played far better of late and now has 8 goals and 34 points in 64 games.