Where is MentionATrueFriend trending?
Twitter

Why is it trending?
It’s a meme.

Background

Twitter users are tweeting to mention a true friend, and using the hashtah #mentionatruefriend.  Tweets vary from those, like @Gee_upinsmoke and @LSoloSaid who are tweeting about actual friends, to others mentioning religious figures or even corporate brands, as TheIncredible1d did when he tagged Ben & Jerry’s, Pizza Hut and Chicken Nuggets.