When you spend an excessive amount of money in order to look wealthier than you are.
Guy 1: "Hey, you heard Griffin bought a Gucci belt?"
Guy 2: "Hey, you heard he spent his whole paycheck on it?"
Guy 1: "Oh. He's false flexing."
When somebody flexes with items that they stole from somebody else
"Hey! Did you see Sidh's new AirPods??"
"No, he's just false flexing-he stole that from coach"