A/N: I don't own Merlin. This just kinda popped into my head after me and Mam had a conversation about onesies.
Merlin was still in bed when Arthur barged into Gaius's chambers.
"Where is that lazy idiot?" Arthur demanded at the physician.
"I thought he was with you." Gaius said.
"Don't try and cover for him Gaius. Excuse me." Arthur stomped up the stairs and slammed open the door.
"MERLIN! Get up!" he walked to where his, still, sleeping manservant lay and proceeded to pull the covers off. He gaped at his sleeping manservant. With a look of confusion he walked back down the little steps leading to the room and approached Gaius.
"What is it sire?" Gaius asked the young king.
"Why is Merlin wearing a sheep to bed?" he asked the older man in confusion.
"A sheep sire?" Arthur pointed towards the door and said,
"Go and look." Gaius stood up with a groan and walked up the steps. Walking into the room where his ward slept he noticed that Merlin was indeed wearing what appeared to be a sheep. The man himself was still asleep even though he no longer had his blanket since Arthur had pulled it off. He decided to shake the man awake. When that didn't work he walked out of the room and walked towards a bucket.
"Excuse me sire. I'm going to go and fill this up to wake up that fool." Arthur grinned and said,
"Allow me." he stood up and walked out of the chambers. Gaius smiled this was a perfect payback for Merlin using his magic to make him think he had gone to tend to the king. Arthur came back a few moments later with a big grin.
"May I?" he asked. Gaius smiled and followed the king up the few steps. As they entered they saw that Merlin was still asleep. They tiptoed towards the bed, Arthur on one side and Gaius on the other. Arthur hovered the bucket over Merlin's head and with an evil glint in his eye tipped it over his manservant. Sitting bolt upright in bed coughing and spluttering Merlin glared at the king,
"What was that for?" he demanded. His hair was sticking to his forehead and Gaius started to laugh at him.
"That Merlin was payback for being late! And why are you wearing a dead sheep?" Merlin looked confused for a second,
"I'm not wearing a dead sheep. This is called a onesie."
"A what?" Arthur demanded. Merlin rolled his eyes,
"Its an all in one. You wear it to bed. Obviously. They're really comfortable." Merlin rattled on and on. Arthur rolled his eyes,
"Merlin! Where did you get it from?" Merlin frowned for a second,
"I don't know. It was just lying on my bed…"
"So you just decided to wear it?" Gaius enquired.
"Yes." Merlin got out of his bed and crossed his arms. When neither of them moved he said, "Well?"
"What?" Arthur demanded as he looked at the full picture of Merlin in his onesie.
"Get out. I need to dress and do the monumental list of chores Arthur has been thinking of since I was late." Arthur and Gaius left the little room and waited for Merlin to appear. As soon as Merlin appeared Arthur pulled him out by his overly large ears as he shouted bye towards Gaius. Gaius chuckled as he conjured another onesie with dragons on it. He wandered through the castle to Arthur's chambers and placed the item of clothing onto his bed with a smile.