Helen wrote: in Oz they would have to know the meaning of "G'day!"

When hiking abroad I try to find out what is an acceptable greeting for people we meet on the footpaths (US: 'trails'.) Sometimes I will know or can guess their nationality, but if not it's best - certainly polite - to use the country's language, which can be tricky. In Greece I would use 'kali mera', say, to a cafe owner but learned that 'yassus' get's a more friendly response from local farmers.

Here in England I vary my greeting according to the age of the person I address. 'Good Morning' (or afternoon) is fine for older folk but tends to elicit a quizzical look from younger ones, as if they expect me to start a conversation. 'Hi' is safe in all circumstances - and best around noon. Young people often resond with 'how are you?' or 'how you doing?' - which is not a question.

As for the original glasses sentence, I wouldn't call it 'wrong' to a student - most people would infer the probable meaning - but it's not correct English. It would be a 'learning opportunity'!