Rude!

So today Brandon gave me some money to take the kids out to lunch. I ended up picking up a salad (really not that healthy, it's still fast food)for me at Jack in the Box and a couple of kids meals. (Which actually had some really cool toys. Big sidewalk chalk and a cool flying airplane.) Anyways, I also wanted to take the kids at the park and eat lunch there. So I did. I ended up going to Vincent Lugo Park which is the one that has the sea monster theme. They have other equipment there and a wading pool for kids 6 and under. (Might do that next time.) The kids ended up running the opposite way I was seated at the table eating. So I turned around so I could see them. They were clear on the other side of the park but I still had a clear view of where I could see them. I just watched them from a far and tried to finish eating. A little in front of where the kids were playing was a couple sitting there facing me. I wanted Sophie to come eat or play on the equipment that was closest to where we were sitting so I got her attention and waved my arms for her to come. I signaled by pointing to the play ground that Ethan had ran to play at. She saw me and did what I said. But now that I think of it more, I think maybe the couple was thinking I was signaling to them. But they did see us all sitting together at the table and my kids playing... I don't know. Anyways, the kids came back to eat, but then Ethan took off running to the other playground where I couldn't see him good and Sophie then followed. I ended up grabbing my purse and leaving the food there so I could go get them. While I was over there getting the kids I noticed the couple get up to leave. They then walked over to our table and I saw them hovering for a little while and then the guy threw something in my salad. I was shocked. After finally chasing Ethan all over the playground I went back and found that he had thrown his empty pack of cigarettes in my salad. I was so appalled. I asked another couple who were kind of close to where we were sitting to see if they saw where they had went. Yes, if they were around I would have confronted them with the kids. Don't have a clue why they would do this. They looked about my age. My kids weren't around them and we did nothing that I could see wrong. I guess they were just rude immature people.
I had another experience like that with a bagger girl at the grocery store. I just was checking out like normal. I could tell that her and the cashier were kind of teasing and flirting back and forth. I just did my thing and paid. The girl had something she was hiding and she didn't notice I saw her slip it in my bag. It wasn't by accident. I knew that because I could see her out of the corner of my eye. Before I left the store I checked my bag and pulled out what it was. It was a rotted out pineapple top. The spiky part all molded. I ended up pulling it out before I left and put it on the shelf right by the door. I kind of was upset so I called the store and saw the manager answer the phone from my car. I told him what happened and where I had left it. He talked like he was really busy and didn't care. Oh well. What I think happened is that the cashier dared the girl to do it. So she did. Again rude and immature. I wish I would of brought it back and said "I didn't pay for this." Too late for that. Always a good comeback too late. I also had Ethan with me and didn't want to deal with it.
Has anyone else experience something rude like that or done something like that for fun or because of a misunderstanding?
I guess maybe there are a lot of negative immature people in this world. I like to think there aren't. I like to think there is more good caring helpful people out there. Like the lady and her daughter at the beach. I guess they'll always be the negative with the positive. I'll just try to be the nicest positive person I can be. Hopefully those rude and immature people will get it. Someday.