Lil Nas X was born Montero Lamar Hill, and Call Me By Your Name
is the title of a 2017 film starring Armie Hammer and Timothée Chalamet as lovers in the '80s. In the movie, Hammer tells Chalamet, "Call me by your name and I'll call you by mine."
As he explained in a Genius video
, Nas saw the film not long before he had a tryst in the summer of 2020 when we was working on music. He got invited to the guy's place and fell for him hard. With the movie on his mind, he started writing the song the next day, and used the famous line in the film as the hook. So he's calling the other guy "Montero" in the spirit of romance.