Well, Olivia Wilde just learned the hard way to not mess with Justin Bieber.

The 29-year-old star of "The Incredible Burt Wonderstone" -- in theaters Friday -- visited "The Tonight Show with Jay Leno" on Tuesday, where she confessed that one innocent little tweet has made her the target of some pretty angry Beliebers.

A few weeks ago, the Biebs was seen walking around (cold) London without a shirt, and out of concern for the 19-year-old, Olivia tweeted: "Bieber, put your f---ing shirt on. (unless you lost all your shirts in a fire in which case my condolences and please purchase a new shirt.)"

Oh no she didn't.

Needless to say, Wilde was then inundated with "35 million" tweets from furious fans ... and they're hysterical.

Watch the video below to see Olivia recount the story and read some of the Belieber responses, including name calling and asking if she's a lesbian.

Keep it classy, Beliebers!

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