Backstory[]
The leadup to Dwight and Andy's duel started when Dwight continued to have sex with Angela, Andy's fiancée. Phyllis finds this out in Goodbye Toby and reveals it to everyone but Andy in Moroccan Christmas. Andy is told about this in The Duel, and challenges Dwight to a brawl to see who is Angela's rightful man.
The Fight[]
Dwight saunters out into the parking lot at the agreed time with a long black whip as the rest of the office watches from the building's window. Andy doesn't appear for a few minutes, not even after Dwight taunts him.
Suddenly, up in the building, Dwight and Andy's coworkers gasp. Andy, who is parked in a nearby parking space, starts up his car, which is silent because he moves it ever so slowly across the lot towards Dwight as the latter reads the note, oblivious.
When Andy's Toyota aligns in the parking spot, it powers on and slams into Dwight, who is now pinned between the car's front bumper and the hedged gate of the building's lot.
Because Andy didn't speed, Dwight is fine, and the only things Andy gained from the sneak attack was making Dwight stationary. When Andy screams at Dwight if he will give up, Dwight says no and starts to lash out on the Toyota's hood, denting it a bit while telling him to get out of the vehicle and face him like a man.
Andy counters with squealing, "I am a man! I'm a bigger man than you'll ever be! A man will never sleep with someone else's fiancee!"
Dwight retorts with, "You're not a man! You don't know how to take care of her! All you do is dress fancy and sing!" Dwight strikes Andy's car again and starts to "La-la-la-la-la!" in a ridiculous lolling voice. "What does that mean? You can't even protect her!"
Andy responds heatedly. "Protect her from what? Bears, you idiot! When's the last time you've seen a bear in Scranton?"
"Last year, idiot!" Dwight shouts incredulously, mockingly, and loudly all in one ball of fury before whipping Andy's hood again.
Jim steps out and confirms that Dwight is okay, apart from a leg that's starting to fall asleep. Dwight and Andy shoo Jim away and continue on screeching at each other, Dwight using his whip to repeatedly bop Andy's car and Andy using his horn and drowning out Dwight's voice.
Eventually, Andy yells, "I don't get how she could be sleeping you this whole time while she only slept with me twice!"
Surpisingly, this catches Dwight off-guard. "What? She's sleeping with you?"
"She's my fiancee!" Andy replies.
Dwight looks crestfallen. "She said she was only sleeping with me."
Andy puts his head on his steering wheel and groans before the camera cuts out.
The Aftermath[]
Andy walks in to the office soon after, seeming defeated. Angela looks concerned when Dwight comes in too, looking equally dismayed. When Andy cancels Wedding Reservations and Dwight seems to be sitting at his desk as usual, a tiny grin grows on Angela's face, but it drops when Dwight chucks a present from her into the wastebasket. Both nonverbally break up with her, leaving Angela unsure of what to do.