Then take your dishes to the designated trash area. Especially when it's busy.

I was at a AF mexican restuarant around noon, Saturday. It was packed. It was difficult to find open tables. I noticed a man wearing BYU fear with his sons. They eventually left but did not bother throwing any of their crap away. There was a garbage can with a clearly marked "thank you" and please clear your tray sign not more than 4 feet from him.

Sorry, my pet peeve of yesterday.