Now when my son has a rough time with not getting his way, I simply have to tell him, "Has Rock Brain taken over your brain?" as opposed to, "You can't always get your way!" He knows what it means, he knows that when Rock Brain has taken over, he uses his Superflex strategies to defeat Rock Brain. (It helps that he's a boy and loves superheroes.) This takes the blame off of him (who wants to change when you feel like you can't do anything about it?), doesn't make him feel like he can't do anything right and allows him to regroup, understand that he's being stuck on his way or the highway and figures out how to overcome the challenge.
Even when he's in the right, he now understands better that how you express it is going to affect how people react. It certainly works a lot better than telling him these things in plain words. Kids start to tune that stuff out until you say it in terms they care about.
When he's throwing a temper tantrum over something silly, instead of yelling at him, I say, "rubber chicken" and he instantly knows what it mean. It means he's not behaving well and he's getting a rubber chicken for his bad behavior. They even have rubber chickens if you need the actual chicken.
Check them out here.