I debated a vanity plate for a long time.  Main reason I chose not to is the cops.  
Here were my ideas
PORQPNE or PRQPINE
for those of you who know about the diff between BMWs and porcupines
this is my first post so I won't post this naughty joke here
UHATEME
saw this on a web site of suggestions, claimed it was on a 325
PORIDGE
as in don't mess with papa bear's porridge
BRKMYWLET
The real BMW acronym - Broke My Wallet, but too many chars
IRIGHTI
Right between the Eyes (recycled plate)
also
on the following link I also found the following
http://www-chaos.umd.edu/misc/plates.html
14THBCH	One for the b**** (or maybe beach), on a white BMW convertible
1MONPAY	One month's pay, on a $105,000 BMW 850Csi
8ISEXC	Ai

't I sexy? Seen on a BMW
BMRMAN	On a 93 BMW 
CLICHE	On a BMW!
DZBLND	Dizzy Blond, on a white BMW in Colorado with a blond lady driver
EGOTAG	On a BMW 325
FNOMNL	Phenominal, on a BMW 318is
IOMOM	Seen on a new BMW with a teenage male driver
LE BMER	On a pretentious white 535i BMW
PD4BYEX	Paid for by Ex-(husband), on a red BMW
RVO3VOM	Move over mirror image, on a BMW coming up at 80mph
SEEYA	On a very fast BMW