Some are even calling it "racist."
But, I think the reader comment below from the Wall Street Journal's Speakeasy blog rebuts the criticism very nicely.
“Sarcasm is the lowest form of wit, but the highest form of intelligence,” – Oscar Wilde. Scientific proof has emerged in the past few years that understanding sarcasm requires social intelligence lacking in people who’ve suffered damage to a section of the right brain. So I must conclude that any “controversy” regarding this advert must be attributed to right brain damaged individuals. As a born and bred “Yard Man” now living in the USA, all of unoo (You plural) need fi relax and hol’ (hold) a meddi (meditation) … in other words “Chill Winston”