Customers are increasingly empowered in their interactions with firms. Sometimes they help firms but, unfortunately, they can also become “toxic” and hurt them. Customers are toxic when they engage in deliberate and potentially harmful acts towards a firm driven either by a reparatory or damaging mental state following a transgression. Whilst the existing literature has studied customers’ negative actions against organizations, critical questions remain as to how and why customers become toxic. We structure a fragmented field of research on customer toxicity and explore customers’ mental state before they decide to do nothing (non-complainers), avoid the brand, act against firms with either a reparatory mental state—and, thus, often constructive in nature (e.g., to initiate change)—or with a toxic mental state and destructive objectives (e.g., to harm and punish a firm). We highlight that the impact of these actions on a firm can still be “toxic” even without intention of harming and punishing. Furthermore, we outline the conceptual domain of customer toxicity and shift the focus from negative behavior to customers’ mental state, by integrating the marketing, aggression, and psychology literatures. We discuss the theoretical implications of our study and explore how future work may further examine organizations’ interactions with toxic customers. Finally, we provide managerial recovery techniques depending on customers’ mental state at a particular time.