In finance, out-of-pocket is synonymous with cash on hand, liquid assets. Means you can pay now without needing to incur a debt.
In business, out-of-pocket is usually synonymous with out-of-office, like AFK Away-From-Keyboard. Often shorter term than being fully on vacation. “I’ll be OOP after 2pm for a doctor’s appt.”
I have recently heard out-of-pocket used among youngsters or the terminally-online to mean rude or crazy, like you said. “Beyond the standards of normalcy”.