Sam could no longer restrain himself from acting on his dark temptations. He grabbed the collar of Dean's shirt and roughly pulled him into a kiss. The kiss was passionate but quick, and it left Dean frozen in shock. When Sam pulled away, he was terrified of what Dean would do. He thought he deserved whatever punches his big brother dished out. This was taboo after all, and Dean couldn't possibly reciprocate Sam's feelings. Or so he thought.
But, to his astonishment, Dean smiled and teasingly said, "Sammy, that was a terrible kiss. Here, let me show you how to kiss the right way." Before Sam had time to react, his big brother pulled him into a kiss that erupted with years worth of desire and passion.
He felt Dean's tongue touch his lips, demanding entry. Sam was more than happy to cooperate, opening his mouth just enough for Dean to explore it. He felt like he was melting from the intensity of his brother's tongue. Then, Sam felt a hand entangle itself in his hair, pulling it just enough that he let out a soft moan. He felt Dean smirking against his lips and his hair was tugged on again. The same soft moan was let out involuntarily, to his embarrassment.
"Well, I found one of your kinks. Now, how should I use this discovery?" Dean said with a cocky smile. He gave his little brother's hair a harder tug this time and the result did not disappoint. The moan was much louder and he could see the passion exploding in Sam's eyes. Dean shoved him against the wall, roughly forcing his tongue back into Sam's mouth. He wanted to stay like this forever, to keep Sammy all to himself. He let his tongue memorize Sam's entire mouth, afraid that he may be dreaming. Dean was clinging on until he had expelled all oxygen from his body. He gently stroked Sam's cheek as they broke apart for air and said, "See? That is how you kiss."