Government Attic queried various states for their lists of forbidden license plates, and has begun posting the results.
The most striking quality of the lists are their sheer size: states ban words with wild abandon, from misspelled swear words (COKK, banned in Ark.) to French drinks (COGNAC, unacceptable in Az.) and network engineer humor (FTPLOL, no go in D.C.), including countless variations. They are also, however, wildly inconsistent, missing obviously scandalous terms. Many disallowed words seem completely nonsensical, too, as if generated by poorly-tuned character substitution apps.
BOINGER, I regret to report, is banned in Arizona.
Here's the lot in one giant PDF. [Government Attic. Thanks, M!]