Identity, or peoples’ situated sense of self, can be conceptualized and operationalized in a myriad of ways, including, among others, a person’s gender, socioeconomic status, degree of expertise, nationality, and disciplinary training. This study conceptualizes identity as fluid and constructed through social interaction with others, where individuals ask themselves “Who am I?” in relation to the people around them. Such a discursive conceptualization argues that we can observe peoples’ performance of identity through the close reading and examination of their talk and text. By discursively drawing boundaries around descriptions of “Who I am,” people inherently attribute value to preferred identities and devalue undesirable, “other” selves. This study analyzes ten workshops from the Toolbox Project conducted with graduate student scientists participating in the Integrative Graduate Education Research Traineeship (IGERT) program. The emotional tone, mood, and atmosphere of shared humor and laughter emerged as a context through which collaborators tested the limits of different identities and questioned taken for granted assumptions about their disciplinary identities and approaches to research. Through jokes, humorous comments, sarcasm, and laughter, students engaged in three primary forms of othering: 1) unifying the entire group against people outside the group, 2) differentiating group members against each other, and 3) differentiating oneself in comparison to the rest of the group. I use action-implicative discourse analysis to reconstruct these communicative practices at three levels—problem, technical, and philosophical—and explore the implications of group laughter and humor as sites of “othering” discursive strategies in graduate students’ efforts to negotiate and differentiate identity in the context of integrative collaboration.