I do not think its earth shattering or anything, but it is without question disrespectful, and I do not think a team should allow that from a player (Any player) to any coach, but it is probably something handled out of the media eye and I think that should be the end of it.
In my opinion it does make Lynch look very selfish and when your team is winning, that should be the most important thing, not worrying about padding your stats.
I see a lot of people get on Manning about that, but I guarantee you he would never give any coach the finger or be disrespectful because they called a run not a pass, disagreements between coaches and players happen all the time, but I think he went a little far with how he reacted and he made a public display of it.