My "mean" phrase is "(Name), we DO NOT (hit, kick, sit in flowerbeds, etc.) at daycare! You need to (stop, apologize, sit for time out, etc) right now!". And then, threat of all threats
, if they're not doing what they need to do "You are NOT listening to my words. If you do not (do whatever), I will HELP you do it!". I'm still not completely sure what that means, but it seems to work really well
I've been using that threat for the past 11 years, and it works every time!
I do like to specify though, that whatever rule is being broken, is the rule we have at daycare. That way there's no room for excuses like "Mommy doesn't make me do this", etc., and it gives parents a way out if they have different rules at home.