Adrien Broner -- Cuffed in Vegas for Fashion Felony (VIDEO)

Boxing champ Adrien Broner was handcuffed and detained by cops in Las Vegas Thursday night, but not arrested ... and his people say it's all because an "a**hole security guard" didn't like the way he was dressed.

People in Adrien's camp tell TMZ Sports ... the 3-time world champ and 7 members of his posse went to Tao nightclub in the Venetian and plunked down $11k for a table. They say the host took the money and let them in, so they took the escalator up to the club and then things went south.

They say a security guard stopped them and said they had to leave because they weren't dressed properly, claiming their jeans and shoes were a deal breaker. Adrien got pissed and said it was hip-hop night and Fabolous was performing, so they were not only dressed appropriately but others were wearing the same thing.

The guard wasn't moved and ordered them to leave. Adrien refused so the guard called the cops.

Police came, cuffed Adrien and took him to a room. His people say police held the boxer for 20 minutes, let him go and then Adrien and his crew left the hotel.

Check out the video ... you hear Adrien say, "They're mad 'cause I'm rich" ... something that seems to be a theme when Broner meets cops.

Broner was arrested in Ohio back in January for DUI. The boxer humblebragged to the arresting officer he was "blessed" because he made more than $100 million in his career. He pled not guilty and the case is pending.

So far no comment from Tao.