I deposited a check from a customer and the bank has returned it NSF. How do I book this in my accounting system?

Just reverse Bank dr and consumer cr

Just reverse Bank dr and consumer cr

Backwards.

An NFS check means that you deposited a check into your bank account and the person who wrote that check bounced it. So their bank sent it back to your bank. Since it bounced on their end, your bank is going to take it out of your account.

Something coming out of your account is crediting cash. And whoever wrote it owes it to you, hence a debit to A/R.

If this is a real situation (not homework), I would call the customer to find out the situation. If you think it's safe, try depositing it again. You should be able to deposit it twice.