Dirty Diaper in a Plate?

So when is it ok to leave a dirty diaper in a dish at a restaurant?  I work as a server and tonight I was thoroughly disgusted.  Not only did the patrons at my place of employ let their kids grind crackers into the carpet, but as I was cleaning up the table after they left I found a dirty diaper in the plate.  What makes that ok? I'm convinced that they hate me.  Actually, this is not the first time it has happened either.  Although, I have been there for 12 years and it has only been about three times...still.  I know when my kids were babies I wouldn't even leave a dirty diaper in someones trash for fear it would stink up the place.  I would tote around those scented bags and just put it in the diaper bag and then throw it away when I got home.  Not just the diaper but the crackers were bad too.  They were little crushed into millions of pieces and it looked like they had just spun around with the bag so the crumbs were good and spread out and then danced in them.  I know I am not the best server ever, but I don't think people think when they go out to eat sometimes.