(someone) thinks (they) are so smart

Someone is not nearly as intelligent or witty as they believe or would like others to think. You think you're so smart, with your fancy degrees and six-figure salary, but you wouldn't know the first thing about how to survive out in this part of the world. Sarah thinks she's so smart, but she'll be in for a rude awakening when she starts college at Harvard next month. All these pundits want to believe they're so smart, and yet even they can't accurately predict the outcome of an election.