The Castrol motor oil one.. where the guy with the heavy Scottish accent violently whacks people across the back of the legs and says something about, "... think with your dipstick".
That action was depicting assault. I complained by email and later got a message that Castrol had decided to not air that ad in the future. I imagine they'd had lots of complaints from parents who thought it in poor taste for their children to see someone assault another with a steel rod to promote the sale of a product.
Later still, however, the ad returned.