All's not fair for Kim Kardashian ... because her SKIMS store in L.A. was hit by a vandal who defaced the walls with a ton of graffiti -- though cops say they arrested the man who did it.

Check out photos of the West Hollywood locale ... with its white walls covered in black words -- including "we need that" and "Kimmy Bread" -- along with a series of other unintelligible phrases on the wall. Unclear if someone meant any of this graffiti as a shot at Kim or if the white-gray walls simply provided a perfect canvas for a troublemaker. Still, Kim's team is not taking any chances ... we're told they're going to talk to police. TNLA

A spokesperson for West Hollywood Sheriff's Station tells TMZ ... they've opened an investigation into the vandalism which the sheriff's office learned abo

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