Those offended would still call it "racist" because it's about the only way they can oppose it. And if they did go ballistic opposing that slogan, you could expect a full-fledged local MSM feeding frenzy to aid their cause, so much so that it would end up being a national cause celebre for the 'Rats.
This might be something they’d try, but it wouldn’t work. First of all, everything in the current cycle is overshadowed by Anthony’s Weiner flipping off reporters, and Spitzer the sociopath losing his revival bid, Syria and the senior swimmer lady, Prince Edward’s reality show, and other stupid stuff. The LSM can’t just conjure up a feeding frenzy at will; all the stars and planets must align for a feeding frenzy to happen, and the sharks are stuffed on too much junk food to get up an appetite at present. Second, the perpetually offended would have scant material to go on. They do want to go back to the days before Rudy, and they will vote Democratic. I think they’ll predict that the slogan will backfire, and snigger oh-so-smugly, ‘til the election results start coming in. There’s not enough there to translate into sufficient angry chimp noises (there, now that’s a phrase that they’d get upset about, if DiBlasio had used it). There’s also the fear of sounding like a jack-ass, which is what happens when you try to make a feeding frenzy out of a molehill and the sharks aren’t biting it.