Nighty?

So I'm driving into work today (yes driving, working on that) and in front of me is a much-too-large SUV with a license plate that says "Nighty." And I say to myself, "Nighty," what does that mean, or, more importantly, what does the owner intend that to mean? I'm thinking . . maybe they like night gowns, maybe they are trying to say good night, maybe they associate with the night and intend "Nighty" to mean "night-like." In that vein, it's possible that they are middle-age enthusiasts and couldn't fit the K on the plate. It also crossed my mind that maybe they wanted to say "Naughty," but that was already taken. In any case, the message was lost in translation. This is the problem with free vanity plates.