Ashton Kutcher Takes On Party Guest Who Mocks Demi Moore

Ashton Kutcher was all smiles in NYC on Monday night following his successful Broadway debut in which he made the audience roar with laughter while playing the boyfriend of a hilariously neurotic Eva Mendes in Montblanc’s 9th Annual “24 Hour Plays.”

However that smile was wiped away about half-an-hour into the after-party at Crest Lounge's Opera Ballroom.

According to an eyewitness, Kutcher’s co-star and wife Demi Moore was mocked by another party guest, sending her 31-year-old husband into an angry rage.

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“Demi and Jennifer Aniston were happily sitting together in the VIP when this guy starting really obviously making fun of Demi and things like her relationship with a younger man,” an insider said. “It went on for quite a while. Ashton heard it and approached him. At first he thought the guy wasn’t serious and was like ‘what the?’ He then realized he was serious. Ashton lost it.”

We’re told a massive verbal fight then ensued between Ashton and the guest, as Demi, 47, looked very embarrassed over the whole situation.

“It got pretty heated, nobody knew what to do,” added the source.

The Hollywood duo stormed out via the back entrance along with friend Jen Aniston.

Reps for Kutcher and Moore did not respond for comment.

Mind you, Ashton is quick to defend his "don’t-call-me-cougar" wife in any situation that raises eyebrows. The actor recently posted a "cheeky" pic of Moore bending over in a bikini on his Twitter account, then scolded those who thought he went too far.

SLIDESHOW: Celebrity Cougars vs. Celebrity Pumas.

"Let's back off a notch. It was a bikini, not underwear so people might have been confused. She was ironing my pants. That sounds weird, but we were on a beach and she was wearing a bikini, ironing my pants,” Kutcher tweeted.

He’s also known for his determination to seek revenge.

Earlier this year Kutcher posted a video of the construction noise coming from his neighbors and said:

“It’s 7:30 a.m. and I get to wake up in my bedroom to my f---ing jacka-- neighbor doing this next to my porch. Right up there, that’s my bedroom. This is where my d---weed neighbor has decided to be building a house at 7 a.m., pounding on steel and welding right next to my frickin’ house.”