Mistah Metro, who works at a New York tattoo parlour, posted an image of his dog on Instagram, clearly showing the animal under sedation, and a tattoo on his shoulder.
In the post he wrote: 'One of the many reasons my dog is cooler than yours! She had her spleen removed yesterday and the bet let me tattoo her while she was under.'
The tattoo is a heart with an arrow through it, with the names Alex and Mel emblazoned across it.
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Although the tattooing of an animal is not illegal, doing it for any other purpose except to identify it to others is not something that animal rights groups condone.
Twitter users expressed their disgust at the tattoo - calling for the dog to be taken away from its owner.
'How does a vet let u tattoo ur dog while still under anaesthesia?? Pic is either edited or you're sick and shouldn't have a dog!' said one user.
'I genuinely hope you never work again,' said another.