Grimes' tattoo is a bold move -- one ya gotta make to shock people with tattoos these days ... so says a celebrity tat artist who has been around the block a time or two.

We caught up with Mark Mahoney -- a pro who's been practicing his craft for nearly five decades -- and we showed him Grimes' new controversial tattoo ... which is basically a big red circle that looks almost like a scar around her eye. Instagram / @grimes

Mark -- who has tattooed stars like David Beckham , Lady Gaga and more -- says even a small tattoo on the arm used to shock old ladies at the store ... but, in today's culture, shock from tattoo is reserved for the wild and crazier ideas -- which he thinks might be the reason Grimes decided on this design.

Mahoney says part of the fun of tattoo is to shock pe

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