A slightly different question, but not off topic. (and no it's not about me).
What if you went on holiday to some place where marijuana was legal and you smoked some, then came back and obviously weren't under the effect any more but got selected for a random drug test which showed positive; what could happen to you?
Apart from the obvious lack of ability to see consequences (see, I didn't say lack of judgement) you did it legally and you were not under the effect. Could you be fired/fined/grounded/etc?
BTW, I passed my random drug test, though I had to guess at a couple of them.