I agree with you in principle, but after having a kid who, without wanting to go into too much detail, requires my constant attention, I can understand parents losing their cool. Thankfully, I have never done it myself, but I have definitely been close to my breaking point a few times already.
Look, all I’m saying is that I have stopped judging parents as easily as I did when I didn’t have any kids. The guy might be an ass to them. Or he might not be. I just dislike people jumping to conclusions as fast as they are.