Posing with porn star Andy San Dimas -- while wearing a UNICORN HEAD -- has a Pittsburgh cop in huge trouble, but San Dimas claims the whole booty-shaking mess is a giant misunderstanding.
This all went down last weekend during a Pirates game at PNC Park, where Andy says she was doing her best to get on the jumbotron ... by shaking her ass in cut-off shorts, while wearing a unicorn head mask!
Awesome, right? Wrong ... because Andy says when an usher asked her to sit down, she tried to rile up the crowd by shouting back, "Oh, I'm sorry I was trying to have a good time at the f**king Pirates game!"
Not smart ... Andy was hauled off to the Pittsburgh PD station at the ballpark.
Andy says the cops were very friendly, and told her they had to boot her from the park -- but not before one officer asked to try on the mask.
Not smart again. That "unicorn cop" is now reportedly under investigation. It's unclear if it's the unicorn mask, the porn star -- or both -- that got him in trouble.
Either way, Andy says she hopes the cop doesn't get screwed ... since he was totally professional and "did nothing wrong."
MLB STAR ANDREW McCUTCHEN
Honey Boo Boo!!!
10/17/2012 5:30 AM PDT BY TMZ STAFF
Pittsburgh Pirates superstar Andrew McCutchen loves Honey Boo Boo. HE LOVES IT. And he's not afraid to admit it.
McCutchen -- who recently signed a 6-year, $51.5 MILLION contract with the Pirates -- was strollin' through L.A. Live yesterday ... at the same time a Carrie Underwood concert was going on.
McCutchen swears he wasn't at the Underwood show (though he says he is a fan) ... but fessed up about his obsession with the "Honey Boo Boo" show.
He even told us his favorite scene ... and it involves snot.