Kim Kardashian is teeing up laughs with Will Ferrell ... he stripped down for a hilarious new SKIMS campaign plugging her underwear line and his new golf comedy.

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Kim's usual eye candy takes a back seat this time ... 'cause shirtless and pantsless Will steals the fairway in nothing but his SKIMS briefs, fully committing to his washed-up golfer character, Lonnie, from his new Netflix show, "The Hawk."

Kim's voiceover is the cherry on top, declaring, "His body says retire, his SKIMS say one more round ... built for men who still know they got it!"

Kim and Will have clearly found their friendship groove ... they're starring together in "The Fifth Wheel," and just weeks ago Kim was giving Will a masterclass in taking the perfect selfie.

Looks like Kim found the perfect SKIMS poster boy!