I don't own Supernatural; just my imagination. Enjoy!
Dean thought Cas had thrown him every scenario. He was wrong. The angel had suddenly flown into the bunker, as muddy as hell, if hell was muddy. Sam was sleeping in his room when the incident occurred.
"Why...?" Dean asked from his chair in the library, mouth agape, staring at the mud-covered trench coat, suit, tie, shoes. Even Castiel's face had mud on it.
"Z."
"Huh?"
"The letter after Y is Z."
Dean blinked, then understood. "Oh, no, I wasn't saying the alphabet; I want to know why you're muddy."
Cas looked at himself as if he suddenly realized he was very dirty. "Ah, yes. That is of no import."
"Well, it is, since you're dripping on my clean floor!" Dean exclaimed, seeing the effort put into his home gone to waste.
Castiel looked down. "I'm sorry."
"Don't move, okay?" Dean stood up and walked into the kitchen.
"I guess I'll just wait here then," Cas stated. Dean didn't seem too angry today. That was a good sign.
Dean returned with a white, wet rag, handing it to the angel. "Get your face cleaned."
Cas did as he was told. By the time he was finished, the rag was brown. He gave it back to Dean, who said, "Now take your clothes off."
There was a confused look on the innocent face of Castiel, but Dean didn't see since he returned to the kitchen. Cas was unsure as to what this meant, knowing that taking clothing off amidst someone's library was awkward, but he still stripped anyhow. He was left in white boxers and navy blue socks.
"You can go get some of my clothes," Dean offered when he reappeared, seizing the pile of Cas' clothes. He didn't seem deterred by the half naked angel, taking the trench coat and suit to the laundry room.
Timidly shuffling down the hallway, Cas found Dean's room and his clothes. He didn't know what to do, though. He felt like only Dean should be wearing those jeans, that jacket, etc.
Dean found him. "Cas, aren't you going to get dressed?"
Castiel turned around, blushing. "I, uh, this, um..." he couldn't look his friend in the eye.
The older Winchester sighed, grabbed a black shirt out of the drawer and put it over Cas' head, pulling it down. "So tell me, how did you get so muddy?"
Cas swallowed as Dean then stuck one of Cas' feet in a pair of jeans. "I slipped."
"Very descriptive," Dean responded.
"Really?"
"That was sarcasm," he started pulling up, up, up on the jeans, which sent chills up Cas' spine.
The angel cleared his throat. "I was walking along the side of a road, tripped on a rock, and it had recently rained, so I fell into a puddle. Then I came here."
"'Cause you know that I'd know what to do," Dean clarified, glancing downward. "Zip up your pants."
Cas noticed that Dean had finished dressing him. "Oh," he said, doing as the Winchester said.
"Was that so hard?"
"Um...no."
"Well, don't expect me to do that ever again," Dean walked out of his room.
Cas exhaled, wishing Dean hadn't said that. He wanted to get muddy all over again.