Adrian Grenier Gets Buck Naked to Celebrate His 40th Birthday

The 'Entourage' actor strips down to his birthday suit -- literally!

Adrian Grenier
 literally striped down to his birthday suit.

For his 40th birthday on Sunday, the Entourage alum spent time in the Hamptons, where he giddily cannonballed into the pool wearing, well, nothing.

WATCH: Adrian Grenier Presented With the Paul Walker Ocean Leadership Award

Grenier documented the naked adventure, writing on Instagram, "Jumping into my 40's wearing my birthday suit."

The caption wasn't all cheekiness, however. He also added an uplifting caption about improving the world.

"#makeasplash with me this year and let's make the world a better place together by showing love and compassion for ourselves, each other, and the natural world around us," he added.

MORE: Adrian Grenier Helps Birds Fly

While the Marauders star rarely undresses on social media, he does frequently share inspirational words about the causes he holds dear to his heart, including animal rights and environmental conservation. Last month, the New Mexico native even called himself out for wasting food after enjoying a healthy meal at a restaurant.

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"Here's an environmentalist's dilemma...the food was fine but I'm full and have no one to share it with. I don't want to contribute to the almost 50% food waste in our country," he wrote. 

"But this place uses plastic to-go containers and [I] don't want to further pollute our precious planet and oceans with plastic. I can't wait for our civilization to evolve implement a better food / waste system so that I don't have to worry so much. I'm sorry I was a part of this sad moment. #foodwaste."

Grenier is such a big environmentalist that he was honored by Meadow Walker, the daughter of the late Paul Walker, with the Paul Walker Ocean Leadership Award in June. See a piece of the presentation in the video below.