It just seems straight-out rude, as if the applicant really doesn't care. Still, I believe it could easily happen, just like not dressing properly, arriving late, forgetting your CV, and so on. Unless of course, the job actually involves chewing gum...

It depends on the job. If you are applying to be a waitress in a coffee shop, then it is OK, but you should probably offer the interviewer a piece of gum.

I think it's no manner that chew gum at the job interview in any country. Maybe some employee in particular job could chew gum. But it no politeness when apply the job at a job interview. Think about it, HR'll not hire you whom just meet first time and you do so rude action. MODIFY IT IF MY SENTENCE WAS WRONG, PLEASE ^^

Sure ,especially in China.the behavior should make you a bad impression on the interviewer ,which shows your disrespect to them.