(Urban Dictionary definition)

The frozen and contorted, usually mildly retarded looking, facial expression one makes for a few seconds before they let out a sneeze or when experiencing a "Sneezus Interruptus".

Check out his Sneeze Freeze. Take cover, it's going to be a BIG one!

Dude, you have an extreme squishy face you're sneeze freezing!

Bob: You were going to sneeze but it got away, huh? 
Dave: How did you know? 
Bob: I saw your sneeze freeze.