"I think that it's perceived as kind of a douchey thing to do, but that's why it's funny!"
That's Steve-O -- the man who made getting tattoos of himself on himself famous -- weighing in on Ezekiel Elliott's tat ... and, spoiler alert, the guy LOVES what the running back did!
"Everybody's favorite topic of conversation is themselves," the former "Jackass" star tells TMZ Sports ... "So, why not just celebrate that?"
Remember, Steve-O once inked a GIANT pic of himself on his back ... and in case ya forgot what it looked like, watch the clip -- he showed us how it's aged over the years.