Jason Momoa Says Screw 'Dad Bod' Haters for 40th Bday Party

Jason Momoa is NOT the guy who gives a rat's ass what people on the Internet say -- especially when it comes to body-shaming trolls -- and his birthday celebration proves it.

The "Aquaman" star, who turns 40 on Thursday, was shaking off the haters when we saw him Monday at LAX ... and instead chose to focus on the awesome friends who helped kick off his birthday festivities.

Jason tells us the Guinness Ale flavored cake served at his recent surprise party was "amazing" ... and he has no regrets, even if haters see it as more ammo to call-out his alleged "dad bod."

Yeah, it's ridiculous ... and Jason's clearly paying it no mind. He even says if we're patient ... he'll proudly put more Momoa dad bod on display soon. Fingers crossed!

As we reported ... the ridiculous comments came after he was spotted in Venice with his wife, Lisa Bonet -- and some idiots said the actor looked little more doughy and needed to get back to the gym.

Jason says it amounts to a big nothing, though, and then he was kind enough to humor our cameraman about being his stuntman.

Meanwhile, Momoa will continue to enjoy his life at almost 40 and beyond, surrounded by friends and loved ones ... including Ian Somerhalder and his "Game of Thrones" costar, Emilia Clarke.

Take that, trolls.