"I'm telling on you!"
In the past it's been, "I won't be your friend unless..."
My three-year-old came upstairs crying (and to "tell on" his brother) because his brother had hit him. I sent him back downstairs armed with the words, "please don't hit me, that makes me sad". I'm trying to teach them to work out their problems themselves. Based on their frequency of trips to report the others bad behavior to mom, I'm not sure that they understand the concept.
At least my children are better behaved than this little boy (Really, what is up with the lack of parenting there! I hope those parents were embarrassed enough by the media coverage that they realize they need to buy a book on child rearing).