Cas flinched away like he had been electrocuted when Dean poked him in the ribs. Dean grinned, loving his reaction.
To Dean, the best part of Cas being human was how ticklish he was. You could hardly touch the guy without him flailing and giggling. Tickling him when he least expected it had become Dean's favorite hobby.
"Not funny, Dean," Cas said dryly.
He had been in a bad mood lately. He walked around with a scowl and he was always unhappy. It was driving Dean crazy. It seemed like it had been forever since he had seen him laugh or smile. He wanted his happy Cas back.
"C'mon, Cas," Dean teased. "You have to admit it's a little funny." He poked him in the ribs again, causing another spastic reaction and an eye roll.
"It may be funny for you but it's most uncomfortable for me."
"Alright, that's it," Dean said, affirmatively. "Time to turn that frown upside down."
"Dean, don't -" Cas protested but before he could finish his sentence Dean pounced on him, poking and tickling.
"Dean..." He tried to talk through his laughter, "Dean... St-Stop." Dean had him pushed all the way against the wall and still he showed no mercy. He continued to tickle him while Cas struggled against him but couldn't get away, his fits of laughter rendering him defenseless. After a good minute of resistance he stopped fighting. "Okay... You - You win," he panted.
Dean stopped tickling him but kept him against the wall. Cas was still breathing heavily, but at least he was smiling. "See, there's my smile," Dean grinned. He touched Cas's cheek before drawing him into a long kiss.