The advertisement in the image above is suggesting that consumers are so impressionable that even the very word "diet" is enough to make them accept a product at face-value.
Especially in the light of consumers who sue or attempt to sue the fast food outlets - in this case, it's clearly Mc Donald's that is being referenced- it is suggested that, for example 0.2% less fat is representative of something resembling effort on the part of the fast food giant at helping consumers in their battle against obesity.
The clearly understated percentages - which obviously do not help when a burger is laden with (possibly) 50% fat are mocking the way advertisers grasp at anything in the persuasion game.
The name "Mc Lard" is an indication that actually advertisers think that consumers have stopped reading after "Diet" and the fact that it's a "Mc" means the consumer gets "diet" products or is convinced that it's a diet product - but at the same time it still comes with a burger (or any McDonald's meal). The use of the brand name is mimicking the so-called "real deal."
The irony, advertisers think they can persuade consumers, reflects badly on these advertisers. Obviously the advertisement reveals the opposite of what should be expected in any thing "less" fat. Lard is fat - ONLY fat! There is no "less!"
Suggesting that they have a moral and social responsibility by promoting "healthier" "Less fat" products is meant as a slap-in-the-face to advertisers. They are supposed to be promoting social change, more acceptable eating habits and so on but they are being exposed, through this use of the ridiculous and the absurd, as being lacking in any social conscience.
In the modern day, obesity is a serious issue and mockery of the advertisers' lack of integrity in combating this is clear in this ad. Using color - especially red- increases the effect. The exaggeration suggested by the color red (and the association with McDonalds) and the use of the word "lard"(sarcastically) emphasize the position. The dry humor is evident.