> The same way that as an Australian citizen you don't have to abide by a ban on e-cigarettes in Singapore even if the law is written in a way that says it applies globally.

What? If you're an Australian citizen you are bound by many Australian laws under the concept of Extraterritorial Jurisdiction. This is mostly used to charge for offenses around CSA, human trafficking, etc. but also applies to drug use. While it's very unlikely you'd be charged for violating laws around e-cigarettes, that doesn't mean the law doesn't apply.