Baker Mayfield didn’t make many friends on the 49ers on Monday night.

After the Browns quarterback was thrashed repeatedly by San Francisco’s defense in a 31-3 loss, 49ers cornerback Richard Sherman griped about his opponent’s manners.

“What’s amazing, and annoying, was him not shaking hands at the beginning,” Sherman said of Mayfield, according to “That’s some college s–t. It’s ridiculous. We’re all trying to get psyched up, but shaking hands with your opponent — that’s NFL etiquette. And when you pull bush league stuff, that’s disrespectful to the game. And believe me, that’s gonna get us fired up.”

Sherman intercepted Mayfield during the game’s opening minutes but defensive end Nick Bosa, this year’s second-overall pick, trolled the former Heisman Trophy-winning quarterback shortly after sacking him, mimicking Mayfield’s flag-planting, collegiate celebrations.

Four-time Pro Bowler Sherman said Mayfield needs to “respect the game.”

“You can have rivals, but pay your respect in that moment — especially when you’re young,” he said.

Mayfield, last year’s first-overall pick, had a nightmare outing, completing 8 of 22 attempts for 100 yards and two interceptions. Sherman maintains that the second-year signal-caller has a lot of growing up to do.

“He hasn’t earned anything in this league. How many games has he won? He’s acting like he was the MVP last year. If [Patrick] Mahomes did that, it would be one thing. But he would never do that, because he has too much respect for the game,” Sherman said.

The Browns, now 2-3, have six days to regroup before they’re visited by Sherman’s old team, the 4-1 Seahawks.