Really? Most of them were just various ways of splitting or repaying bills. The loan I will admit might be in a somewhat legally grey area.

Traditionally only if you are charging an interest rate. There are a few rules in the US around lending money to non-family and expecting it to be paid back.

IANAL, but I lend a lot of money, and this is what I've been told:

If you give without the expectation it is typically just cash swapping hands in both directions. If you give money to a non family member and expect payments (with or without interest) OR to a family member and expect more than a rate that is defined at the IRS (<1%, IIRC), then the income is taxable. How they tax you on a no-interest loan to a non-family member, I have no idea.

A no-interest loan to a non-family member is taxed as income to the borrower. They impute an interest rate and say that amount is income since a free loan has a value. I'm not sure what exactly the rate they impute is or how large the loan has to be before they do this.

Ah, that is very similar to if the company you work for loans you money. I'm assuming the rate is probably the same as the max interest rate for a family loan.