During a confrontation with Maverick in a locker room, Ice Man chomps his teeth at Maverick. What was that about? An attempt at intimidation? Catching a fly? It was just so weird and random.
Your first guess was correct - it was an attempt at intimidation. The chomping of the teeth was a common gesture at the time, meant to indicate biting down (like a dog snapping at a bone, or a shark snapping at meat). It could also be a seductive gesture, but obviously - given the context - that wasn't the case.
Iceman was basically saying to Maverick "I'm gonna get ya.", with the implication being that the second Maverick messed up, his rival would be there ready to take advantage of it.