The Hills star arrived at the bash at Pechanga Casino and Resort in Temecula with Lance Corporal Jonathan Burkett, who invited the reality TV star via Twitter.com in August (11).
He wrote, "Wanted to know if you want to go the the Marine Corps Ball with me in San Diego?"
Thrilled Cavallari accepted Burkett's invite just hours after he posted the message, and the star, who is dating American footballer Jay Cutler, turned up to the event in a floorlength silver gown and posed for photographs with the military man.
She told reporters, "I just thought, why not? It’s a nice way to say thank you for everything that he’s done for our country. Seeing the faces of the people fighting for our country, it just puts everything in perspective."
After the event Cavallari wrote on Twitter.com, "Had a great time at the marine ball."
Last weekend (12Nov11), Justin Timberlake accompanied Corporal Kelsey de Santis to a ball in Virginia after she asked him to be her date via YouTube.com.
Following in the footsteps of Black Swan star Mila Kunis and Justin Timberlake, Cavallari will now attend a forces get together after jumping at the chance to join military man Jonathan Burkett at the ball.
Burkett put out the invite via Twitter.com on Thursday (25Aug11), asking, "Wanted to know if you want to go the the Marine Corps Ball with me in San Diego?"
And thrilled Cavallari didn't waste any time, responding, "Would love to! When is it?" hours later.
TMZ.com reports Cavallari is now working out the details to make the date happen.
Meanwhile, Kunis will attend one of the Marine Corps balls as Sergeant Scott Moore's date after he posted a video message invite online from his military base in Afghanistan, and her Friends With Benefits co-star Timberlake will take Corporal Kelsey De Santis to the party.
Audience members at the Kodak Theatre in Hollywood and viewers around the world were puzzled when Elinor Burkett joined Williams onstage and pushed him aside as he started his Best Documentary Short acceptance speech.
Stunned Williams admits he was too shocked to do anything, but now insists Burkett should never have been there after removing her name from the credits of the film following a bust-up over the film Music By Prudence.
Burkett tells Salon.com, "The director and I had a bad difference over the direction of the film that resulted in a lawsuit that has settled amicably out of court. But there have been all these events around the Oscars, and I wasn't invited to any of them. And he's not speaking to me. So we weren't even able to discuss ahead of the time who would be the one person allowed to speak if we won.
"When we won, he raced up there to accept the award and his mother took her cane and blocked me. So I couldn't get up there very fast."
But Williams tells the website, "Only one person is allowed to accept the award. I was the director, and she was removed from the project nearly a year ago, but she was able to still qualify as a producer on the project, and be an official nominee. But she was very angry - she actually removed herself from the project because she wanted more creative control...
"She just ambushed me. I was sort of in shock... I just expected her to stand there.
"She pulled a Kanye and it's a shame, because this is such positive, happy film."
West upstaged Swift at the MTV VMA Awards last year (09) when he ripped the microphone from her to protest the country music star's Best Female Video win over Beyonce.
And, as for Burkett's claim that the director's mother tried to keep her from going up onstage at the Oscars, Williams adds, "My mother got up to hug me, and my mother is 87 years old."