  Social media platforms offer flagging, a technical feature that empowers
users to report inappropriate posts or bad actors, to reduce online harms.
While flags are often presented as flimsy icons, their simple interface
disguises complex underlying interactions among users, algorithms, and
moderators. Through semi-structured interviews with 22 active social media
users who had recently flagged, we examine their understanding of flagging
procedures, explore the factors that motivate and demotivate them from engaging
in flagging, and surface their emotional, cognitive, and privacy concerns. Our
findings show that a belief in generalized reciprocity motivates flag
submissions, but deficiencies in procedural transparency create gaps in users'
mental models of how platforms process flags. We highlight how flags raise
questions about the distribution of labor and responsibility between platforms
and users for addressing online harm. We recommend innovations in the flagging
design space that assist user comprehension and facilitate granular status
checks while aligning with their privacy and security expectations.
