Tara Reid -- My Marriage is BOGUS!!

That wedding Tara Reid just couldn't shut up about -- she should've shut up about ... because she now admits the marriage was never legal.

Tara seemed totally out of it at LAX when a TMZ camera guy asked if she and her husband could win the Newlywed Game.

While not quite, "In the butt, Bob" -- Tara's slurred response was still pretty awesome ... as she confessed she was "never really married."

You might recall, Tara and Zack Kehayov (above) had a surprise wedding in the Greek Isles in August ... which she tweeted about endlessly. Tara says she and Zack never made it a legal union here in the U.S.A.