Henry
Autoexreginated
There's nothing wrong with knowing the rules... as long as you don't attempt to use them to usurp the benevolent dictatorship. 
As long as the DM has final say over any rules questions, then there's not problem with gently reminding him. In my own case, it happens during the game and I don't mind, but some people dislike having the game disrupted in this fashion, even briefly, so it's best to go with the rules of etiquette for your group.
But my personal philosophy is that for the sake of harmony in the game, the DM's word is final. If the DM has to make a final call, the group should stop arguing the point, and agree with it at least until the end of the session. Then, the group may want to re-discuss and decide how to handle it for next session.
There's a time for discussion, and a time to play; it's best to avoid the former until after the latter.

As long as the DM has final say over any rules questions, then there's not problem with gently reminding him. In my own case, it happens during the game and I don't mind, but some people dislike having the game disrupted in this fashion, even briefly, so it's best to go with the rules of etiquette for your group.
But my personal philosophy is that for the sake of harmony in the game, the DM's word is final. If the DM has to make a final call, the group should stop arguing the point, and agree with it at least until the end of the session. Then, the group may want to re-discuss and decide how to handle it for next session.
There's a time for discussion, and a time to play; it's best to avoid the former until after the latter.