Question about cannabis legality/ usage

Okay. Imagine someone goes on vacation to Amsterdam. They indulge in the use of cannabis while their there, and then travel back to the states. They get drug tested at their place of employment and they show up positive for cannabis. Now because they partook in consumption of cannabis in a country where it is legal, and they have the ability to prove that there was no way they could not have consumed it except in Amsterdam is the fact their shown to be positive still legitamate? Could they incur repercussions from the act of consuming cannabis even though they did so in a country where it is legal?

Usually one is bound by the laws of the district in which they stand.

So it would not be against American law for you to smoke marijuana is certain parts of Amsterdam, or wherever, as long as it is legal for you to do so according to the laws there.

But, convincing your employer that you only did it where it was legal and not here and skirting the fact that your job contract has a no pass, no pay policy or some other crap like that, it thats the case you broke the rules you employer set for you no matter where you are.

Then again, interpretation of the law, lawyers, judges, instances, and where you work can all change things majorly for the better or worse.

I dont think there is a deffinetive answer here.

That's what I was figuring. Thanks.