There was a House episode where a prisoner had a low-quality tattoo containing too much iron (or something). The prisoner went into the MRI and the experience was excruciating.
Not sure if there's any grain of truth to that or not. It was Hollywood.
MythBusters covered this one in one of the earlier seasons. They couldn't produce any sort of effect even with unlikely high metal concentrations in the ink.
Metal fabricator of my acquaintance probably can't have an MRI, as he's got too many metal splinters floating around his body. So probably true, though I don't know about tattoos...
Not sure if there's any grain of truth to that or not. It was Hollywood.