What a strange topic to make a first post on, anyway...
Personally, I can cuss up a storm with the best of them, but I do avoid doing it in public when possible.
HOWEVER, I don't think anyone really has the right to invade another person's private conversation just to make editorial comments on their choice of words and I CERTAINLY don't approve of the suggestion that you'd threaten to 'knock a person on their back' for telling you not to stick your nose in their business. I mean, cursing may be something you'd prefer to not expose your child to for as long as possible, but I'd imagine pointless violence, or threats thereof, are a bit worse.
Plus, look at it this way, if you catch someone cursing in front of your kids it becomes a great chance to teach them not to talk that way. A well-worded, "Hey, Bobby, doesn't it make that man sound stupid to say that ugly word here in front of everybody?" should do.
Realistically, there are many worse things our kids encounter everyday.. When you see someone smoking out on the street you don't walk up and tell them not to do it because your kids are there.. You tell your kids it's bad for them (a lot worse than curse words). Same goes for seeing people drunk at WDW (which could lead to cursing. =) ).
Sorry, it just got my hackles up that people would be so confrontational about this instead of things that can ACTUALLY hurt people.