No Smoking
Apple is claiming that using your Mac in smoking households (judged by the tell-tale yellow residue, I’m guessing) voids its warranty. Why? Because it presents a biohazard to the employees working on the machine. Smoking is presently out of fashion, making smokers an easy target1. But nowhere in the AppleCare terms does it specify anything about smoking.
If you want to enforce a rule, first make a rule.
- Disclosure: I quit smoking about two months ago [↩]