"Those are not your balls; sorry, but you cannot play with them." (This one gets me every time; don't ask me how I channel the mind of a 12-year-old boy when it comes to that word.)
"Daddy is using your sippy cup right now. You cannot have it because he has yucky germs right now. I know it's yours, but please share it with daddy." (Good old hubby caught a killer strain of the flu virus and actually needed a sippy cup to drink from because he couldn't sit up.)
"If you put your foot in the dog's water dish one more time ... "
"If you said you have to poop, then you need to go poop!"
"Don't dribble water out of your mouth. You are not a fountain. We swallow our water."
"Honey, don't touch your weenie. It has pee pee on it, and pee is not for your hands. It's for the toilet."
"We only eat two vitamins a day. You can have more tomorrow."
"Do not drop your fish oil pill in the toilet. I will not give you another one."
I think I need a vacation.