Well, I've been reading the replies here, and normally I'd probably start to lean towards your ideas of just leaving the whole thing alone, never mentioning it at all. However, since changing my Facebook picture, about six people I know who aren't too knowledgeable about tattoos have asked me what it's about- three of them being people who were going to make appointments at the local studios that aren't much better than Lisa's "school". I wouldn't have normally talked to them (four were people from high school!) so it was cool that that's opened up a little discussion with them and probably saved their skin from the laser treatment place.
A silver lining, even if it is a small one, is always good.