For a very long time, I've found most vanity plates deeply unsettling. The ones that referred directly to the car itself seemed fine, but plates that made a claim about one's identity -- approximations of phrases like "Daddy's girl" or "Three kids, one male two female" came off to me as incredibly reductionist, and, well, creepy. In retrospect, though, I think I haven't been giving some of those plate types the proper benefit of the doubt. When a license plate is obviously a name for the car, I've been comfortable dismissing it as a description of the car, not its driver. I didn't assume that the driver was trying to encapsulate their whole selves in a single word, especially not where that word was a description of one's station within one's family.
But family dynamics make a lot of impact in decisions about buying a car. A license plate that reads something like "Soccer mom" doesn't necessarily mean that its owner considers that the most fundamental truth about herself. It only really suggests that she felt it was important information about the car.
In the past, I've separated license plates into two categories in my mind: the ones that obviously represented merely an aspect of the person, and the ones that tried to capture the whole. But there's really no way I could genuinely make that distinction -- on reflection, I think the categories I was really extrapolating were: the plates that imply qualities I like or am neutral towards, and the plates that imply qualities I dislike. I was needlessly vilifying swaths of people based on my own subconscious and semiconscious biases.
These sort of things are important when you're an otherwise irritable driver, you know. Anything that makes the trip more stressful makes me more likely to drive like an asshole, and I hate letting myself have excuses to do that.