Things you should never have to say to your roommate... but that I have (with complete sincerity).

"Pull your pants up, please."
"Get your shoes and I'll help you put them on."
"Don't touch the poo!"
"Do you need me to wipe your nose?"
"Woo-eee! Steeenkeeee!"
"That's not a cow-- it's a dog."
"Seriously. That doesn't match. You'll get made fun of!"
"Wipe and flush, please."
"See? Picking up your backpack wasn't so hard."
"We're going to the store. And if you behave I'll give you a treat!"
"Need me to take your shirt off?"
"Can you say 'yellow'?"
"What does the word 'hurry' mean?"
"What does a frog say? Ribbit, ribbit!"

(In response to "what's that?"):
"This is a peanut butter and jelly sandwich."
"It's a sock."
"A person."
"Garbage."
"A car."
"It's your blanket."
"A dog barking."
"Someone coming in the door."
"A cow mooing."
"The same cement truck we've had at the house for the past four months."

(In response to "what are you doing?"):
"I'm watching you put your seatbelt on."
"I'm waiting for you."
"Driving."
"Making your lunch-- like I do every morning."
"I'm changing her pants."
"Singing."
"Well I was trying to ignore you."