MIL “What do you think of tattoos?”
Me “I don’t like them but each to their own”
MIL “X (niece) has got one!”
Me “Oh! What is it?”
MIL “A star on her wrist”
Me “Oh well at least it wasn’t the name of a boy or something!”
MIL “She’s done that as well...”.
Me “Oh.”
Next day MIL tells me she’s told niece that I think tattoos are awful, especially boys’ names blah blah blah and niece and SIL (niece‘s mother) are furious at me. 
I shouldn’t have fallen for it. It’s MIL’s way of telling them SHE doesn’t like them but it was sneaky.