Gay, bisexual, and other men who have sex with men (GBMSM) often use GPS-enabled dating apps and websites to facilitate in-person sexual encounters. Many of these encounters are positive and enjoyable. However, there is limited research on GBMSM's negative experiences with partners from hookup and dating apps/websites, especially those characterized by threats to GBMSM's sexual, physical, and/or psychological safety. In this report, we investigated this matter. We analyzed data from interviews with GBMSM (N = 60) and identified four categories of negative sexual experiences, each of which were comprised by sub-categories: 1) sexual violence (physical sexual assault, verbal sexual coercion, intoxicated assault/coercion), 2) sexual health risk behaviors (condom use resistance and coercion, deception related to HIV/STI status), 3) non-negotiated behaviors (undiscussed/unexpected sex acts, rough sex, sexualized racism, undesired substance use by the partner), and 4) threats to physical safety beyond sexual violence (being blocked from leaving, stalked, robbed, drugged). These results can inform future research and interventions that aim to promote safety on dating apps/websites within the GBMSM community.