Sweet hilarity! Napoleon Dynamite is out to prove to one and all that he's got nothing to prove. How dramatic!
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He retreated leaving scorched earth behind him. This over extended Napoleon's supply lines which were under constant threat by cossacks and required vast numbers of combat troops to be wasted as foragers searching for food and fodder.
To 'fall behind those advancing in front' (see 'straggle/straggler'); 'to develop at a retarded rate in comparison with the more advanced'. Thus the common usage 'to lag behind' is a wordy tautology one should avoid. Where else can you lag? In front? Above? To the side? Being implicit in the meaning, 'behind' is a useless appendage there only to remind the dull-witted of the meaning of 'lag'.
Mad ads are commercials that are designed to get your attention. Often the meaning behind the ad is to get something stuck in the brain of the consumer. A song, or a slogan for example. The belief is, if you are thinking about the ad, you will buy the product.
I believe it is a reference to the Biblical Adam and Eve story where they pick the forbidden fruit from the tree and Sin is created