Trying to live up to your friends' standards can be a costly habit. In fact, it's sending a surprising percentage of millennials into debt.

That's according to a new report from Credit Karma, which found that "nearly 40 percent of millennials have spent money they didn't have and gone into debt to keep up with their peers." They're most likely to overspend on experiences, like going out with friends or taking vacations, Credit Karma notes.

"FOMO spending," or the modern-day version of "keeping up with the Joneses," is tempting. Respondents reported feeling uncomfortable saying "no" when a friend suggests an activity they can't afford.

But short-term spending habits can derail long-term planning, and many millennials are already struggling to hold onto money: A growing percentage have absolutely nothing saved at all.