So at my daughter's bus stop this morning, apparently one boy pulled down another boy's pants. I did not see that happen, I just saw that there was about to be a fight in the street. So when I saw that, I stepped in and said "I am not going to let you do that to each other. There will be consequences for that!" That's when the other boy said well he pulled down my pants! So I said "I'm not gonna let you do that either!" There were other parents around, just not the parents of these kids. Nobody was doing anything. I was looking at them all and they said these aren't my kids and they just minded their own business. But I couldn't let kids hurt each other in front of me. I feel like I did the right thing. What would you do? 

Update: Thank you for your comments! I never know exactly what to say in these types of situations as I am generally nonconfrontational. I didn't want to lecture them because I wanted what I said to be concise which in my experience is usually more effective than lecturing. I also just wanted them to listen, I don't want them to dread seeing me in the morning. They knew exactly what behavior was wrong and why. At the bus stop today, when I walked up, I said "Good morning gentlemen, let's be good to each other today!" And everyone looked at me and said "Good morning, OK." And they did behave. So seeing that, I do believe that what I said was effective. Let's see how long it lasts!