Penn, 37, issued a tearful retirement speech in July 2014, following a one-sided TKO loss to featherweight Frankie Edgar in Las Vegas. It was Penn's third loss in a row.
The legendary Hawaiian is apparently reconsidering that decision, however. In an Instagram post Wednesday, Penn (16-10-2) posted a photo of himself inside Jackson-Wink MMA in Albuquerque, New Mexico, challenging Lentz (26-7-2) to meet him at the UFC event in Las Vegas.
"This is a formal challenge for Nik Lentz to meet me in the Octagon March 5 in Las Vegas," Penn wrote. "Nik you wrote a silly poem about me making fun of me, you said stuff about me and my parents, and you [have] been making a #bringpennbackhastag. I ask you today to be a man and back up everything you said, talk the talk walk the walk, uncle BJ is mad already."
Penn was referring to an online poem Lentz wrote in October, in which he called Penn "old" and a "fat ass." The poem was written in response to a statement originally made by Penn, which centered on Lentz's previous relationship with Penn's former nutritionist, Mike Dolce. At that time, Penn said he wanted to fight Lentz at 145 pounds. Lentz has since fought at 155.
A longtime lightweight, Penn hasn't fought at that weight class since August 2010. He hasn't won a fight since November 2010 and is 1-5-1 in his last seven bouts.