I have to agree with Erwin. You people need to lighten up! If you think smoking a little pot is the worst thing taking place on your cruise, you need to look around a bit! When it comes to breaking the rules, we must also condemn the booze smugglers, chair hogs, dress-code violators, truant children, drunk teenagers, and the ever-popular nursing-at-formal-dinner mothers! Notwithstanding that marijuana use is illegal in the States, those other violations are equally a breech of the rules of ethics and consideration. As for suggesting "have a few drinks instead", obviously YOU are not in the company of recovering alcoholics. Funny how quickly our self-medicating society condemns pot, which BTW is legal and perfectly acceptable in some countries. Just because you don't condone it, don't say nobody else can partake. There are much worse things happening: swing by the casino and see the compulsive gamblers scraping more and more credit out of their accounts; or sit at a bar and watch alcoholics lose control.
TIA, one thing I do agree on is DO NOT try to take it home with you. I assume your friend is planning on having only a very small amount, for their own personal consumption. Just be careful, and since it obviously bothers many folks, be considerate. That said, have a blast on your cruise!!