John likes showers and Sherlock likes baths. No, no. John likes quick showers that are just long enough to get himself effectively clean, probably taught to him by his time in the military. Sherlock, however, likes to sit in hot water and, sort of, float around a bit while he thinks about the case or he's bored. He pretends he's getting clean, which he's not, and basically he's too lazy to stand in the shower.
But today, John was trying to get Sherlock to actually bathe, as in, wash his body, his hair, his armpits, and his feet, which always smelled particularly odd. John didn't know why, Sherlock probably soaked them in some concoction he made himself. They didn't smell bad, but they didn't smell like soap. So, every other day John would try his hardest to get Sherlock to really bathe.
"Come on, Sherlock, just tilt your head back. I'll do it for you."
"Leave me alone, John."
"You cannot possibly think that sitting in your own filth is getting you any more clean than not bathing at all."
Silence. A lot of silence. And staring. John stared at him with an annoyed face, a face he often gave Sherlock. Sherlock liked that face because it meant John actually saw him. Others would just roll their eyes and walk away, but John cared enough to give Sherlock the certain look that said, "I see you, darling, and even though I think you're being ridiculous, I still care enough to stand here and give you this look until you do as I say."
Usually Sherlock complied after the look was given, probably because as much as he liked the look, he knew John didn't.
"I love you," Sherlock whispered as he tilted his head backwards and closed his eyes.
"I know."
"Do you, John?"
"I do, Sherlock."
"Then why do you make me do this?"
"Because, as the one sole person that has to share a bed with you, I'd appreciate it if you didn't smell like dirt and sweat. Stale dirt and sweat, that is. What do you do while I'm at work? Play around a play-ground and sand box? Go down the slide? "
"I'm not a child, John."
"You're certainly not a 35-year-old man."
John scrubbed Sherlock's scalp, which Sherlock loved. If he could die like this he'd be happy. He was never more relaxed or empty headed, which was a strange and unnatural thing for him, and he loved it.
John loved scrubbing Sherlock's scalp because he liked taking care of Sherlock. He liked to make him tea and clean up his messes, he liked to wash his hair and his feet and other areas that always end up being touched after Sherlock is as relaxed as he can be and everything is as un-relaxed as it could be.