The origin of the electron-like events in excess of Standard Model predictions at MiniBooNE remains unknown. Recently, new physics explanations based on neutrino upscattering to unstable states have become increasingly popular. For the first time, we consider a detailed evaluation of the constraints on these so-called dark neutrino models set by the gaseous Argon TPC at ND280, the off-axis near detector of T2K. By recasting a null result in the search for vanilla heavy neutrinos decaying into e+e- pairs, we can exclude most of the interesting parameter space to explain the MiniBooNE anomaly, especially where the lifetimes of the new states vary between a few centimeters to tens of meters.