Late Night Shift Blues

I work the night shift at a local diner. I've been doing it for about three months now because of financial reasons. It pays well and covers my bills, but there's this one thing that happens every single time someone leaves after a meal. They always forget to take their trash with them. Every time. And I'm here in the middle of the night when everyone else is fast asleep, left to clean up after people who were so busy stuffing their faces they couldn't manage to grab their empty bags before leaving. Tonight was especially bad. A family came in and had a huge feast. When they finally got up to go home, not one of them even glanced at the trash on their table or the floor. I cleaned it all up, feeling tired and resentful, but what could I do? Tell everyone off? I don't know if this is normal for night shift workers. Am I supposed to feel so annoyed every time something like this happens? Should I just learn to let it go? What else can you do when people are being careless in the middle of the night and leaving your job dirty?