My opinion has always been, if you don't have the intestinal fortitude to enforce the rule across the board (including with your favorite kids, the kids with the epic nutcase cheer moms, the quiet kids and/or the ones you don't like) then don't even make it a rule.
If you're not going to have a spine enough to say the same thing to EVERYONE (rather than just letting your rule follower folks do it because that's who they are, then stick your head in the sand over the non-rule followers with the crazy cheer moms you don't want to lock horns with) then just don't make it a rule in the first place so the rule followers don't feel like they're the only ones made to actually toe the line while everyone else gets to do whatever they want.
Because for as much as rule followers will talk about how THEY are going to do whatever they want next...since it clearly doesn't matter....we won't. Because we can't bring ourselves to break the rules, even when we want to and know there will be no consequences. Instead, we just get annoyed that no one else has our rule-following character....and no one else is making them have it either.
#endrant