A judge raised her eyebrows and whistled ’15 cocktails, that’ll do it’ as she dealt with a punch-up at upmarket Oxford cocktail bar The Alchemist.

Dylan O’Connor, 21, had enjoyed more than a dozen drinks at the rooftop nightspot at The Westgate shopping centre in the early hours of April 1 when he took umbrage at being called ‘blue cap guy’.

CCTV played to Oxford Crown Court on Thursday (May 25) showed him headbutting his victim. The man was also punched and had a chair thrown at him on two occasions.

Prosecuting, Matthew Knight said the attack left the victim with cuts to his forehead and a chipped tooth.

O’Connor wept in the dock as Mr Knight read an impact statement written by his victim and detailing the anxiety he had suffered as a result of the assault.

“To this day I am careful and conscious when leaving my home, even when going to work,” he said.

He added that he felt ‘startled’ when the post is delivered and had to ‘double check all the windows and doors are secured’ before going to bed.

The manager of The Alchemist apparently offered him a ‘free lunch’ following the attack on him, but he declined it as he did not want to return to the scene of the incident.

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Mr Knight said the defendant and victim were part of different groups that were separately enjoying a night out at the idiosyncratic, science-inspired cocktail bar.

Their early interactions were friendly, sparked by one group asking the other about the ‘bubble cocktails’ they were drinking.

The groups enjoyed ‘general chit-chat’ for around 30 minutes before, ‘all of a sudden’, O’Connor launched his assault.

In his probation service pre-sentence report, it was suggested that what sparked the assault was him being called ‘blue cap guy’.

The judge, Recorder Samantha Presland, noted: “15 cocktails, that’ll do it.” Mr Knight, for the Crown, replied: “15 cocktails, enough to knock anyone sideways.”

O’Connor, of Hanson Drive, Oxford, pleaded guilty at the magistrates’ court to causing actual bodily harm. He had no previous convictions.

Mitigating, Richard Davies referred obliquely to his client’s traumatic childhood, as well as to his deep remorse. He had not drunk alcohol since the incident.

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Imposing 12 months’ imprisonment suspended for a year and a half, Recorder Presland said: “I have read about your childhood and the responsibilities you have taken on in the last few years.

“It is clear that those emotions have bubbled up with a lot of alcohol.”

She added: “You have lashed out in grief and anger.”

As part of his suspended sentence, O’Connor was ordered to pay £500 in compensation, do 100 hours of unpaid work and abstain from drinking alcohol for three months.