I usually mind my business, but his tone and choice of words bothered me, so I stepped in:
Me: "Why are you shouting at kids?"
He: "Did you see what they were doing?"
Me: "Kissing?"
He: "It's bad for your kid to see as well."
Me: "I wouldn't use those words in front of a toddler."
He, irritated: "I'm not talking to you."
Me: "Well, we are all strangers here."
He, fuming: "Calm down."
Me: "I'm not the one shouting at kids."