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.
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.