This book investigates how participants on YouTube respond to and enforce norms of sayability through self-censorship practices. Drawing on a corpus of YouTube commentary videos and their corresponding comments, What the eff adopts an interdisciplinary approach that combines sociopragmatics, media linguistics and linguistic taboo research in order to shed light on the complex processes of censorship and self-censorship in digitally mediated communication. Through an examination of monomodal and multimodal instances of these processes, along with the metacommunicative discourse that accompanies them, this work reveals how participants actively negotiate and challenge what can and cannot be said on the platform, highlighting the dynamic and contested nature of online discourse in algorithmically controlled settings.