Do they follow US laws or HK Laws on those flights?

CAUTION!! The wrong answer here could well lead to leventy-seven hundered more posts "just wondering" whether it's Johnny Walker Black or Green, whether the the glasses are round or square, whether the tray tables on the A340 are the same size as on the 747, whether the napkins that go under the glass are the nice off-white ones or the nasty beige ones, whether the drink menus are printed in a standard or italic typeface, whether the ice cubes are solid or have holes in them, and whether drinks are served in the same order as meal orders are taken.

Probably HK law, which can mean anything..

Honestly, to anyone below 21.... anyone above 30 is OLD! :p

Well, I don't like to drink alcoholic beverages anyway. Yes, I have tried them.....

HK law applies. It explicit states "over 18 only" on the wine list/drink menu.

I remember CX in its safety video says about smoking in lavatories ("will be subject to HK law and will be fined up to HK$5000"). I guess companies such as SIA would have Singapore law apply to their flights, Air Canada, Canadian law and so on. It sort of works on the principle of a embassy or consulate's land is their own.

I believe, as was stated above, that it is the prevailing law of the airline's home country. HKG law on CX, British law on BA, US law on the US carriers..

M