The parents in the stands that seem to know it all regardless of their non-existent, or very limited coaching experience (at best) are everywhere. If you don't think they exist in your program, chances are really good that they're just quieter than most other places.
How to deal with those type of parents will depend on which coach you ask and their experience with them, but this letter from a coach to one of those know-it-all parents was so good that the coach had it framed and over a decade later is reflecting back on it and sharing the experience with the rest of us.
Some will say it may fall a bit on the passive aggressive side of things, while others are going to read it as a stroke of genius. Whichever side of the line you fall on, I think we can all enjoy and appreciate this approach at least a little.