Three men are facing life sentences for killing an IT expert after snatching his girlfriend's Halloween hat.
Ben Gardner, 30, was punched to the ground where he lay helpless as one of the men kicked his head "as if taking a penalty".
Allanna Devine, 28, was also punched in the attack on October 31 last year, the Old Bailey heard.
Daniel Ransom, 21, Ross Collender, 21, and Jordan Dixon, 18, all of Carshalton, Surrey, were found guilty of murder by 11 to 1 majorities. They were remanded in custody until sentencing on Friday.
Mr Gardner, who worked for insurance firm Legal & General, had been to a club with Miss Devine to celebrate her birthday and Halloween last year. She was dressed in a pirate's outfit, with a black wig and hat. He had a black leather jacket and vampire fangs.
In the early hours of the morning, Miss Devine was waiting for Mr Gardner outside a kebab shop in Sutton when a group of men snatched her black hat and wig.
Miss Devine broke down as she spoke of Mr Gardner's last moments. She said: "My hat and my wig were taken from my head. I was not concerned about it because it was the end of the evening, but I did say 'Can I have my hat back, please?' I was greeted by jeering. They were very loud."
She said: "Ben decided he was not happy that my wig and hat had been stolen and he was going to approach the group about it."
Brian Altman QC, prosecuting, told the court that CCTV footage showed the incident unfold. He said: "As Miss Devine went to pick up a black witch's hat which had been thrown by someone unconnected into the road, Dixon booted it away. Ransom kicked and stamped on it and, in a quite provocative and contemptuous act, spat in it and threw it at her."
Then Collender "suddenly and unexpectedly" punched Mr Gardner on the left side of the face, said Mr Altman. As he recoiled from the blow, Mr Gardner was punched by Dixon and fell on to his back in the road. Mr Altman said Ransom then kicked an "utterly defenceless" Mr Gardner.