I was once playing with a tennis ball with my dog and another dog at the park the other day - they were getting along really will playing with the ball together and the was only one other dog there who I knew so I was comfortable playing with the ball. Anyway, I reached down to pick up the ball at a wrong time and the other dog accidentally nipped me while trying to play with my dog. I instinctively let out a yelp (that's my signal to my dog that she can't nip me - it's worked well with her, this is just a lingering reaction). I felt so bad that I accidentally reprimanded someone else's dog. The owner was concerned that I got hurt, and I had to explain it was reactionary and apologized that I just tried to discipline their dog. My point is, that aside from a "no" or a turning away from a dog jumping on you, there is no room for disciplining someone else's dog. I don't know how that other dog reacts to my yelling or what it's past is. If I am concerned about a behavior I talk to the other owner like an agile or just leave.