Take some of my bitcoin for custody, please.
A bank:
1. Sure, send it to this address.
(Some time later)
You:
Give me back some of my bitcoin, please. You may send it to this address.
The bank:
1. Where did you get it, mofo?
2. Do you have a written proof of it's purity followed by a notarized affidavit?
3. What are these satoshis sent from multiple wallets of dubious origin, eh?
Your story was incomplete. I took the liberty and fixed it.