: In LGBTQ+ and ballroom culture, "to clock" someone means to recognize or identify them as transgender when they are attempting to present as cisgender. This is often tied to "reading" or noticing subtle traits that reveal a person's trans status.
The phrase combines two terms—one a slur and the other a slang term—primarily used within LGBTQ+ contexts, often with derogatory or harmful intent. tranny big clock
Clock It! How Ballroom Coined the Internet's “New” Catchphrase - Them : In LGBTQ+ and ballroom culture, "to clock"
: Because of the slur involved, using this phrase is generally considered an act of harassment or transphobia. : In LGBTQ+ and ballroom culture