In group discussions, people rely on everyday diplomatic skills to socially regulate the interaction, maintain harmony, and avoid escalation. This article compares social regulation in online and face-to-face (FtF) groups. It studies the micro-dynamics of online social interactions in response to disagreements. Thirty-two triads discussed, in a repeated measures design, controversial topics via text-based online chat and FtF. The fourth group member was a confederate who voiced a deviant (right-wing) opinion. Results show that online interactions were less responsive and less ambiguous compared with FtF discussions. This affected participants’ social attributions: they felt their interaction partners ignored them and displayed disinhibited behavior. This also had relational consequences: participants experienced polarization and less solidarity. These results offer a new perspective on the process of online polarization: this might not be due to changes in individual psychology (e.g., disinhibition), but to misattributions of online behavior.