[Tallest]

Generally speaking an M5 conversion is so expensive that you will rarely see one (and it is pointless because you have a slower version of the real exact looking thing). And to debadge an M5 to make it look like usual car is also so much effort no M5 owner will bother. Quads, brakes, fenders, grilles - all together probably show you what you got in front of you. I do like the look of some of the M5 components - rims and grilles. But even then, Im on the fence about adding those. Just something doesnt feel right though frankly speaking I think its a fair game. Only like 5 people will be able to tell what comes from where, and you are on a BMW forum and even you had to ask. So fair game.

On a side note, OP, if that guy really bothers you so much tell it to his face...