To flex means to boast or show off about something. The phrase 'weird flex but ok' is said when someone proudly boasts or brags about something that most people would find either
awkward,
irrelevant or just plain
weird. It's usually stated in a dismissive fashion.
Girl 1: "I'm dating my firend's
dad, if we ever get married I'll become her stepmom!"
Girl 2: ... Weird flex but ok.
Person 1: "Yo, I finally hooked up with my
cousin on
Thanksgiving."
Person 2: ... Weird flex but ok.