I'm thinking that the thing to do is to be prepared; design mobile scale units which take into account your height, and whatever other factors are there so then Obesity agents can cruise around pulling people over, force them to get on the scale and instantly have a readout of the degree to which they are off of the prescribed mark. The fine would be automatically computed.
I know it is coming, so I figure if I have the cool design for such a vehicle, I'll sell tons of them to the various levels of government who choose to be involved. Of course, NYC may be the first on board, but California hates to be out nannied so they may press ahead in some surprise move.
I don't care, I'll sell to anyone. Of course I expect the agents to be armed and dangerous, so I'll take that into account. I may have the option of installing something akin to a cow catcher on the front so they can scoop people into a sling scale set up as they walk down the sidewalk. Maybe smaller electric versions for malls and park paths. This will be fun and lucrative.