I'm not sure that person meant that the obese should be made to pay more in automobile taxes specifically, but rather in health insurance premiums, or some other kind of fat excise tax.

I'm of the opinion that, assuming that a licensed medical provider has performed an appropriate evaluation that excludes the diagnosis of an underlying metabolic disorder that specifically causes one to be obese, there should be remuneration made to the health system for the consequences rendered by their behavioral decisions.

Theres already precedent for this with tobacco use.