Trust me, I was on the verge of saying something to them multiple times. And, I do have a hair-trigger temper.
But, I've been around long enough to know nothing good would have come of it ... other than an ego boost for me if they actually stopped with the trash talk. Highly unlikely, though. And, I doubt it would do much good for how they speak at home.
I'm no Puritan and drop my share of f-bombs around my kids, but nowhere near the extent these people did in public.
They need to be confronted by a cop to get the message.