Usually, Sherlock tried to stay in his semi-human form when he was around John, It really took very little for him to keep the other shape.

But when John said that, he went to his normal form, 9 feet tall, long, lithe, and clawed.

"As you wish." He growled evilly.

He took himself in hand, long and teased John's entrance, almost pressing in, then pulling away. He hadn't prepped or stretched John the first time, and he wasn't about to this time.