Some layman people are against special relativity and stubbornly persist on their theories. One man put the model that the speed of photon is c + v, where v is speed of source. In such case Michelson interferometer is not a good anti-argument. What is, in your opinion about the most simple and effective experimental or theoretical argument against the above model (for educated non-physicist.) He wishes an experiment, where source of light is moving. I gave an argument about the speed of OPERA neutrinos, but argumentation is not easy. All physics is against the above model, but anti-argumentation is not easy.