Can they? If a person from France uses weed in California, will France get mad?
Seems kinda silly to enforce a country's laws on someone even when they're in another country. I guess social media makes it kind of a gray area though, since the violating act might be the upload itself (which can happen anywhere and is essentially 'continuous' even when the uploader returns to their home country).
It depends on the law where you're from. US citizens are sometimes surprised that they can be prosecuted by the US for crimes they've committed abroad, even when it's not a crime in the place where it happened. The term for this is "extraterritorial jurisdiction".
> Seems kinda silly to enforce a country's laws on someone even when they're in another country.
It's relatively common these days. The US assumes global jurisdiction for anything that touches the US Dollar (as e.g. Kim Dotcom of Megaupload has been fighting for years now), and most Western nations assume global jurisdiction for a select few grave crimes (mostly murder, war crimes and sexual exploitation of underagers).
They could. An American could say unsavory things about the Thai monarch in New York and end up getting into trouble when she travels to Thailand years later.