Mykelti Williamson -- Bubba's Got Beef with Bubba Gump Shrimp

Mykelti Williamson won't step foot in the restaurants named after his most famous character ... because he's got issues with corporate giant Viacom.

Of course Mykelti played Bubba in "Forrest Gump" -- which inspired the Bubba Gump Shrimp Co. chain of restaurants, so we brought it up with him at LAX on Tuesday ... only to discover he's NEVER eaten there.

MW first told us how he celebrated the recent 20th anniversary of 'Gump' -- but quickly launched into a rant about the movie studio's parent company and its ties to the restaurants, and big oil ... of which he's not a fan.

Only problem is he's mistakenly referring to Gulf Western Oil, which has nothing to do with Viacom. A company called Gulf + Western DID merge with Paramount (and eventually Viacom) ... but is NOT an oil company.

Glad we could clear that up. Now make a reservation, Mykelti.