Disclaimer: this is all lighthearted, and your relationship with them is not as enemies.

Sherlock

His heart...and a picture of him when he was 12 and he tried to straighten his hair, but it just looks like shaggy, loose curls.

John

He kissed another guy for a dare once, you have a picture on your phone.

Mycroft

The receipt to the treadmill. He doesn't know how you got it, but you keep it crumpled up in your pocket. You wouldn't really try to use it against him, you just mention it whenever he gets on your nerves.

Moriarty

Nothing, sorry, you cannot blackmail him.

Molly

You don't really blackmail her, but she gets flustered when you bring up her past crushes/infatuations.

Lestrade

You know he has the receipts from your first date, and the stubs from the first movie you saw together.

Irene

The passcodes and passwords to all her locks and phones. She's tried changing a few just to test you, but you've gotten them right within 3 tries.

A/n: I'm working on a book for Sherlock that's one shots, imagines, preferences, etc. are there any scenarios you'd like to see more of, or any characters or ships?