If anyone on this list is likely to go full Rick Genest, it's Jack, since she's about 9/10 of the way there anyway. So tattooed that some people actually think she's wearing a shirt, Jack apparently did most, if not ALL of her art herself, making her that much more badass. If asked the right questions, she'll tell Shepard her ink symbolizes a wide swathe of things, from prisons she's escaped, to people she's killed, to times she just felt like getting a tattoo and you can fuck off. Anything more specific than that, though, is left up to speculation.
As flippant as Jack can be, body art is one of the few things she takes seriously. If Shepard pursues a relationship with her that lasts through Mass Effect 3, in place of a sex scene she'll tattoo him, making sure he can be identified if he's injured or killed in battle. That's… remarkably sweet, for her.