In a home tournament. Basics: All stacks >100BBs. UTG1 raises to 3BB. MP1, MP2 and Button call. I am in the BB with AKo. I re-raise to 18BBs. Folds to the button who calls. Button is crazy loose extremely passive player. Flop comes J 7 4 rainbow. I cbet ~1/2 pot and get called. Turn misses me. I decide to give up on the hand and check. Villian checks back. The river misses me and I check again. The villian then says "its yours" but throws his hand in the muck face up. His hand is 48o. He clearly has my ace high hand beat but his cards are in the muck, face up, but in the muck.
What's the rule here? What is proper etiquette?