Grocery Store Etiquette

This may seem simple, but apparently a reminder needs to be given: the person in front of you gets to put their items on the conveyor belt at the checkout before you. Last night I stop at the store to pick up a few items--not many, so I did not bother with a basket. the gentleman in front of my saw me carrying my small load and kindly adjusted his items to make room for mine. As he placed the divider down, I flashed a 'thank you' smile and was about to put down my first item when the A-Hole behind me decided to start chucking the items from his basket up in the limited space (yes....I do been chuck as in hurtle, throw, toss rudely). I was at a loss for words, which I shouldn't have been...in hindsight I should have told him to move his crap. The man in front of me looked amazed as well. When I got to the cashier of course he made the mistake of starting to ring up what was on the belt before I could hand him my things and tell him the other stuff wasn't mine. What happened to common courteousy? I hope he chokes on his can of spam!