I know someone who had the plate 1-DERFUL.
Also, the guy who used to own a certain well known convenience store in town had:
VII XI 
Years ago I heard of a set of vanity plates that backfired on the owner.
I was working on the computer systems for the County Welfare dept, and heard this story from some of the elegibility technicians there.
A lady had her fairly-new big black Caddy outfitted with the plate “ON WLFR”, and drove it around town. Annoyed a lot of cops, who pulled her over for various minor traffic offenses. One of them reported this to the office, with specific details of the car, who held the title, etc. The ET investigated and determined that she had not included this vehicle in her listing of assets. And that with it added, she was over the limit, and not longer eligible for the welfare program she was on. So they pulled her eligibility, effective immediately. And the ET’s (who saw a lot of struggling families who really needed help) were annoyed enough to call me to ensure that the check for the next month (already in the computer process) got pulled.
So she may have had fun with her plates for a while, but it cost her in the end!