I've had several vanity plates and haven't had an issue. For the M5 I have "PFFT AMG" coming. My car friends (several of whom drive AMG cars) get a kick out of it, partly because we make fun of some of the slightly less intelligent/sensible idiots who drive them and always want to street race.
I guess it just depends on where you are.
2014 X5 xDrive50i ZMP - Alpine White/Mocha (On Order)
2013 Tesla Model S P85+ - Gray/Black (Sold)
2013 F10 M5 (Sold)
2013 Cirrus SR22T