Using Venmo sometimes feels like making a deal with some personal-finance devil. Venmo gives you an embarrassingly convenient way to send money to friends, and all you have to offer in return is perpetual access to your most private banking information. It's a potentially precarious arrangement, but for the most part, it works astonishingly well. What happens when it doesn't?

If you're the kind of person who splits rent with roommates, frequently dines out in large groups, or has a recreational drug habit, Venmo is a fantastically hassle-free way to make payments. It is the rare internet startup that actually provides its users with a useful tool, rather than an attention-sucking advertisement delivery service disguised as a platform for connecting with friends. So why does Venmo insist on being a terrible social network, too?