The actor – who's promoting his new film, Nymphomaniac, at the Berlin International Film Festival – arrived sporting a shaved-down tooth and disheveled appearance for the cast panel, answering only one question before quickly exiting the room.
When asked how it felt to be in a movie with such explicit sex scenes, LaBeouf took a drink of water and said, "When the seagulls follow the trawler, it's because they think sardines will be thrown into the sea."
The actor, 27, then thanked the audience, got up and left.
It was a reference to a situation with soccer star Eric Cantona from 1995, in which he spoke the same exact quote prior to walking out of a press conference, according to the Hollywood Reporter.
LaBeouf's Nymphomaniac costars, including Uma Thurman and Christian Slater, looked stunned by his sudden departure – although they recovered quickly with a joke.
"Obviously, the script is packed with a lot of sardines," deadpanned Slater. "One sardine after another."
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Although the actor wore a natty suit to the world premiere of his film, he paired it with a cut-out paper bag over his head that read, "I am not famous anymore," a line he has been Tweeting daily since Jan. 13.
This caps a month of odd behavior from LaBeouf, who also reportedly lunged at three men that tried to take a photo of him Saturday night, which followed a recent fight at a London pub.
In January, the actor was also embroiled in a plagiarism scandal with author Daniel Clowes, to whom he later apologized before Tweeting that he was retiring from all public life.
Reporting by MICHAEL ANHALT