Thanks to xNomii for the prompt.
"Don't b-be rid-d-iclulous, Merlin," Arthur bit out through chattering teeth. "I'm n-n-not that c-cold."
"You're blue skin begs to differ," Merlin said, torn between amusement and annoyance. "But suit yourself. I'm not the one who's freezing his arse off. I had the sense to wrap warmly."
"Well I d-didn't know w-we'd get stuck in this c-c-cave!"
"Nor did I. I still bought warm clothes."
Arthur just glared at him.
One minute passed, then two. Finally, Arthur burst out with "Fine! This blanket is hopeless! Come over here!"
Merlin smirked.
By the time the snow storm had cleared hours later, neither of them were wearing any clothes and both of them were very warm.