Let's watch, and see if we can spot the problem:
So what was the issue? Implied zoophilia? Encouraging food-based adultery?
According to the BBC:
The Advertising Standards Authority (ASA) said: "We also examined the size of the burgers in the hands of an average-sized man and considered that they did not fill the hands to the same extent as the burger featured in the advert.
"We concluded that the visuals in the advert were likely to mislead viewers as to the size and composition of the product."
This is pretty funny, considering everyone knows they don't use real food in ads. Right?
(Example from nuffy.net - there are more disturbing ones!)
Plus, of course, everyone also knows we men exaggerate the size of everything we can get our hands on.