So today I was out with some friends and DD and DS in our local park. There was a dog - collie crossed with something else I reckon - bounding around unaccompanied in the park and diving in and out of the playground area from which dogs are banned. I was a bit 
as it was very busy with lots of small children around and I have never seen anyone just leaving their dog there like that before.
A bit later, as we walked past the tennis courts, we noticed a mum with her three kids freaking out because this dog had cornered her son (6yo-ish) and was growling and barking at him. She was trying to get her scared son to walk to her and her DDs and every time he moved the dog would get a bit closer and stop the kid from moving. The dog was obviously getting scared and excited too and my friend very bravely went and caught it by the collar and calmed it down enough for us to have a look at its tag and phone the number that was on it.
It turned out that the owner was in the playground around the corner with her kids and was very blase about her dog having been running around and bothering people and told us to just let him go again. 
The woman with the kids in the tennis courts was really upset by now - it was her having the phone conversation - so I took the dog and marched down to where we could see the owner and told her that I was absolutely not going to just let him go.
She got really angry with me and told me that I was "ruining her day" so I pointed out that that her dog had ruined the day of the little boy playing tennis and how did she know that the dog wasn't crapping everywhere while she wasn't looking. She then told me that it's a very safe dog and that she's got two kids of her own, but imo there's no such thing as a "safe" dog when they're stressed and scared and unaccompanied. I asked her why she couldn't just put the dog on a lead while her kids were in the playground - which is what most people do, and tie them to the fence - and she said that "he doesn't go on a lead" She then left her toddlers unaccompanied in the playground to go and put the dog in the car and asked me if I thought that made her an irresponsible mother as well (and I said yes, which was horrible of me, I know).
I told her that she was irresponsible and horrible and rude and that she shouldn't have a dog if she wasn't able to control it. I might have been just a bit fucking furious by this point.
I also told her that if I saw it unaccompanied and annoying children in the park again then I would call the police which, I admit, was maybe just a bit OTT
So I know I over reacted but who was most U, me or her?!