[Simon knows that face, as it is usually when one of his own family members takes him aside and handles things. He hopes a strange man won't go amiss here, and he makes sure to have his own gem (a sapphire) visible.]

[The hospital gown looks enough like the ones he's seen in the human world (well, via television and advertisement) to place the young man as being from a world similar to his own.]

I think we can find a shop that should have some ready-made.