Square. It's a bloated mess of a company still trying to "pivot" after its idea of being the credit card middle man never really took off (or took too long and allowed others to catch up, depending on how you see it). They're doing a bunch of different things but nothing that really seems to stand out. Have you seen anyone use Square Cash? Squareup? Didn't think so.

Quora. I'm surprised YC even took them in. It has an overwhelmingly unmonetizeable userbase (primarily in India). It's growing and growing but there's nothing really that can justify the $900mm+ valuation if there's nothing to monetize. I also personally hate their pesky model that_forces_ you to sign in to view more than a single answer. Maybe Yahoo will buy them and quietly kill them at a lower valuation in a few years.