Holmes would laugh at his eagerness if it isn't so contrary to his plans, and so therefore he can't find it amusing. He gives Watson an entirely disapproving look instead and takes the towel back.

"You had better find your patience," he returns, a challenge to his voice, and he advances on Watson until he has him backed against the sink. It's effort to draw away from him; in fact, he indulges and kisses him, but only briefly, before he makes himself take a step back.

"You took your time; I intend to take mine."

He shakes out the towel and starts to dry Watson off, scrubbing the fabric over his chest; he's sure to hit the sensitive spots, to brush over his nipples, to linger over his hips. He gently towels off Watson's cock before he gets to his knees to do his legs.