Millennials are the worst in a survey that found 36-million Americans have had a bad experience lending their credit card to a family member or a friend.
Matt Schulz at creditcards.com says nearly half of us have let someone use our card.
"You're really playing with fire when you let someone else use your credit card."
Schulz says it's okay to lend your card -- but you have to make some things clear.
"What you really need to do is, you need to make sure you communicate the expectations and make sure that everybody understands the consequences up front."
Schulz says the bottom line is the bottom line -- you are responsible for the charges on your card, no matter who actually does it.
"You've got good intentions, probably, loaning the card but the truth is regardless of who does that spend on the card you are the one who ultimately has to pay for it, so be careful."
It appears wisdom comes with age; the survey found Millennials are the most likely to make this mistake and Baby Boomers are the least likely.’