Peyton Manning -- T-Shirts in the Pool ... Ain't Just for Fat Guys!

Peyton Manning has not officially decided if he's coming back to play in the NFL next season, but one thing is for sure ... the Denver Broncos QB needs to retire that t-shirt!

The future Hall of Famer and his family were spotted poolside in Miami Beach this week, where the QB committed the personal foul of wearing a shirt in the pool ... a move usually reserved for offensive linemen.