This book explores how variants of "I'm not a/n..." function as a linguistic strategy in web forums, revealing how users present themselves while negotiating shared interests. It starts from the premise that identity is not fixed but performed in interaction, shaped by situational and sociocultural factors. In disembodied online communication, negative self-identification positions speakers in relation to their claims and highlights relevant identity categories. Through a corpus-based study, this book uncovers patterns of meaning-making and guides readers through conducting research in discourse pragmatics. It will be of interest to students of English linguistics, scholars in applied linguistics, and anyone curious about the links between language, identity, and the social world.