Hi doma,
There are all sorts of clever arguments about all sorts of things. The cleverness doesn't depend upon the object under discussion.
But in this case, I said seemingly clever. It seemed clever because at first glance, it looks like there's a logical rationale. Cyclists do emit more CO2.
But once you look carefully, you can see the rationale itself is not very thoughtful. But you have to figure why.
The argument isn't wrong because "it is outrageous". It is wrong because it takes no account of the carbon source, the carbon cycle and the net carbon emission of the cyclist.
As it happens, the cyclist is already paying the tax the argument demands. He pays it in the price of the extra food he consumes to fund his carbon use while cycling. And as dig pointed out, this food consumption partly depends on hydrocarbon energy employed by farmers in their production process, who then pass their costs along to consumers.
The cyclist pays for the carbon tax one munch at a time. The tax is in his mouth on the way in rather than on the way out. Tastes a bit better that way,
I think the person who shared his idea was a politician rather than a person with any kind of government authority.