No way. Nope. Nuh uh. It was not Sam's fault. It was all Dean's fault. 100% Dean's fault. Although, Sam wasn't exactly doing a good job of complaining about it. In fact, he quite welcomed it. It was still totally and entirely Dean's fault though and Sam was entirely and wholly innocent in the whole thing...
"Dean... you've kissed hundreds of people, I hardly doubt I'm the best." Sam pressed lazy kisses to the corner of Dean's mouth, trailing them along his jaw, nipping every so often. Apparently he was about as confident in his kissing skills as he was in his looks - not very.
After all, growing up watching Dean, having Dean as a role model... Dean was like a Kansas Casanova, where as Sam was always the awkward puppy.