Ahahaha. You can thank my friend Lothus for this idea.
Disclaimer: I don't own FMA. I do own Roy's apron though.

One harmless joke. One stupid little harmless joke.

That dumbshit Mustang should've known better. And after sending him on such a stupid mission, too.

"This is my punishment?"

"Yes, Fullmetal. You'll stay here and tend to all the work, every task, until I feel you've paid up for your little.. prank."

"Oh come on! How was I to know you're such a glutton and were gonna eat ALL of those cupcakes?!"

"YOU SHOULDN'T PUT LAXATIVES IN CUPCAKES!" Roy yells, throwing the apron at Ed. "Now get to work!"

Ed growls in irritation as Roy leaves. He looks around at the kitchen. Roy's kitchen.

"That dumb bastard.. if I bake him cupcakes with laxatives, you'd think he'd know better than to put me on kitchen duty as punishment. Frickin' idiot!" He tosses the apron onto the kitchen table, walking to the sink to find dishes inside. "Great. This will be just awesome for my automail."

"Stop complaining, Fullmetal," Roy says, walking into the kitchen. "Put the apron on and get to work."

"I don't want to wear your damn apron," Ed growls in irritation.

"It's not a request; it's an order.

Ed grumpily throws on the apron, turning to tend to the dishes. However, as Roy speaks again to stop him, he bristles in annoyance.

"That can wait, Fullmetal. After all, why not do all of the dishes at once?"

"They're all here, you dumba-"

"But you'll be making more very shortly."

"..What?! I'm not COOKING FOR-"

"No, you're not cooking, don't worry."

Ed calms a bit. "Good. There's no way I'm-"

"You'll be baking."

Ed's golden eyes widen, contrasting greatly against his reddening face. "LIKE HELL I WILL BE!"

"You don't have a choice. Unless you'd like me to tell Hawkeye about your little prank."

"The Lieutenant?! Why would she care about-"

"She ate one of the cupcakes!" Roy yells. He then points to the stove. "Now make me some cinnamon-sugar cookies!"

As Roy turns and heads out, Ed flips him the bird, crossing his arms as he glances at the cupboard. "How the fuck do I make these? I never made cookies in my life." He opens the cupboard, grumpily yanking out whatever he thinks goes into the cookies. He soon has a collection of ingredients, and once he finds a bowl and spoon, begins combining and mixing things. "I hope this makes him sick. Serves the prick right."

Half an hour later, the scent of cinnamon wafts throughout the house, surprising Roy, who is reading in the living room. {He's actually making them? Well, I'll be damned.} With a smug grin, he gets up to go check on Ed.

Ed spots Roy walking into the kitchen, claps his hands, and forms his automail blade. He points it at Roy threateningly. "They're not ready get! Get out!"

"You do realize this is my kitchen, in my home," Roy replies, stopping to casually watch Ed.

"No, right now this is my kitchen. Now unless you're here to relieve me, get the hell out."

Roy shakes his head with a small smile. "Carry on, Fullmetal." He turns, giving a careless wave as he heads back to the living room.

Another half hour passes, leaving Roy's stomach growling. "Hurry up with those cookies Fullmetal, before I-"

"Before you what, Colonel?" Ed asks, startling Roy.

"Don't sneak up on me like that!"

"You call this sneaking up? For the love of.. I have boots on. I have a noisy automail leg. How the hell did you survive the war?"

Roy glares up expectantly at Ed from his seat on the couch. "Cookies?"

Ed sits the cooled tray on Roy's lap, revealing golden-brown cookies with a thin layer of frosting on top. "Enjoy," Ed says with a sneer.

"I'd better." Roy lifts one up, popping the entire thing into his mouth. The first thing he notes is how soft and pleasantly gooey it is. The second thing..

He spits the cookie out into his hand, making a gagging sound. "Fullmetal, that's AWFUL!"

"Sorry, I'm a bad cook," Ed says, a wide grin on his face.

"I would possibly have believed that, if it weren't for the fact that there's a full half inch of cinnamon layered on top of an otherwise good cookie pretending to be frosting."

"It's not PRETENDING to be frosting! More is better, isn't it?" Ed pauses. "..Isn't it?"

"If that was true, you wouldn't have tried to claim you were a bad cook, now would you?"

"I claimed that from the look on your face when you ate one!"

Roy shakes his head in disbelief. "Less cinnamon. Do it again."

"Like hell." Ed picks up one of the cookies, shoving it right into Roy's face before turning and walking out of the house, taking the apron with him.

"FULLMETAL. Get back here before I tell the Lieutenant-"

"Go ahead and tell her! Just see if you can make it out of the house for five minutes!"

"What are you talking-... you didn't."

"Right in the icing!"

"I'm going to torch you."

"You're too easy, Mustang!" Ed cackles, running off.