Ex Giants Star Steve Smith -- Titans QB Needs to Drop His Phone, Pick Up His Playbook

EXCLUSIVE

Retired NFL star Steve Smith is taking Titans QB Zach Mettenberger to task for that gameday selfie he took before taking a loss against the Texans.

Mettenberger's been getting blasted by fans and players for the Instagram of his new haircut -- hours before Sunday's kickoff ... his first start, by the way. Smith says the kid needs to be more like his ex-QB, Eli Manning.

Smith was shopping in Calabasas when he stated his case ... and it's a good one. Ever seen an Eli or Peyton Manning selfie? Exactly. And Steve's got hardware to back up his argument.

Speaking of which ... you gotta see Steve's jab -- at his OWN Super Bowl ring! Michael Strahan would not approve.