I've always found it interesting, and extremely amusing, that they call them "vanity" plates:
van·i·ty ( P ) Pronunciation Key (vn-t)
n. pl. van·i·ties
1. The quality or condition of being vain.
2. Excessive pride in one's appearance or accomplishments; conceit. See Synonyms at conceit.
3. Lack of usefulness, worth, or effect; worthlessness.
a. Something that is vain, futile, or worthless.
b. Something about which one is vain or conceited.