The $R_K$ measurement by LHCb suggests non-standard lepton non-universality (LNU) to occur in $b \to s \ell^+ \ell^-$ transitions, with effects in muons rather than electrons. A number of other measurements of $b \to s \ell^+ \ell^-$ transitions by LHCb and $B$-factories display disagreement with the Standard-Model predictions and, remarkably, these discrepancies are consistent in magnitude and sign with the $R_K$ effect. Non-standard LNU suggests non-standard lepton flavor violation (LFV) as well. We discuss several $B$-physics observables to measure such LFV effects.