I used my business account (bank or credit card) to pay for personal expenses. How do I categorize these transactions?

If there are personal expenses charged to your business bank account or charged to your business credit card, you would categorize these to Loan Payable - Owner. 

This literally translates that the business has loaned $ to you since the business paid for your personal expense.

On a related note, when you give your personal $ to the business (i.e to pay the business' bills), you would categorize this cash inflow into your business as Loan Payable - Owner. In this case you are loaning your business money in order to pay the business bills.