But the courageous tree surgeon, decided to step in and confront the thug who was punching a man unconscious outside a pub in Stourbridge, West Mids, in October.
His feat of bravery is all the more remarkable given that Karl, 30, was wearing only a caveman costume when he opted to save the day.
CCTV footage shows Karl, armed only with his inflatable club, storming over in disgust to scare the thug away before staying with the battered and bruised victim until an ambulance arrives.
Just moments before the attack, the victim was pushed to the ground before the thug rained blows on his face and continued to kick him in the head.
Last week, the disturbing footage made headlines around the world after police released it in a bid to trace the attacker.
But modest Karl, from Hagley, West Mids, said he was just trying to be a good citizen.
He said: "For some reason my friends went out the front door and I went out the back.
"That's when I saw the man being kicked.
"There were three men attacking him. I wanted them to stop so I went over and asked them what they were doing.
"One of my friends called the police and ambulance to help the injured man.
"It was really horrible. It was one of those moments where I was thinking 'was that real?' I couldn't believe it had happened.
"The man was badly injured but I am glad he's recovering well.
"I was just trying to be a good citizen and I hope somebody would so the same for me.
"The first thing I knew about the footage being released was when my sister text me to say she had heard it on the radio.
"I couldn't believe it when I saw the video - it was everywhere. Out of all the things I could be wearing it was a dead caveman costume.
"We had decided to wear fancy dress because it was almost Halloween."
Detective Constable John Horrobin, from West Midlands Police, appealed for any witnesses to come forward: "In the footage you will see a couple of people in fancy dress costume.
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"There had been a fancy dress party at the Mitre Inn on that night and we are appealing to anyone that may have seen the victim on the night to come forward.
"If you saw the assault we would also like to speak to you – ultimately we are hoping that someone will recognise the attacker and will come forward with a name.
"The victim has little recollection of the attack and thankfully he will make a full recovery."