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>Is this meant to be ironic or am I totally missing something?

I think if you note the claim that a homemade PB&J sandwich costs $3, as well as the reference to "extra bicycle fuel", you will have your answer.

Not to mention that a bike's wear and tear on the road is exponentially less than the damage incurred by a passenger car or SUV: http://en.wikipedia.org/wiki/Gross_axle_weight_rating

You are correct, if you are talking only about pure efficiency. Your parent was talking about (ironically or not) cost. At current market rates, peanut butter is inarguably a more expensive fuel per Calorie than gasoline.