In hockey, when a player fakes a forehand shot on goal, but instead of taking the shot, swings around the net, and takes a backhand shot on goal which enters the net in the top corner.
'muck', most likely derived from the sound of hockey skates on ice.
', a sticky, delicious substance, used in this instance due to it's ability to stick to roof of one's mouth and temporarily incapacitate an individual.
'top shelf', refers to the placement of the puck in the net, particularly the top corner.
Commentator: "...he moves to take the shot, but wait, he's faked out the goaltender, he swings around, takes the shot with a backhand slap and... muck muck peanut butter top shelf
, he scores!"
Crowd: /raucous applause/