On Social Graces:
Q: I was recently at a wedding, seated next to my significant other’s 36 yr. old son. He was chewing gum and I politely and in a rather joking manner, as we have a close relationship, mentioned that I didn’t think it was either the right place or time. However, he answered that it’s perfectly acceptable these days. Was I ‘way off’ the mark here?
A: The “rules” of gum chewing ought to be confined to private times or the company of close friends—not during class, at work, or in worship services, and not when in conversation. Therefore, your significant other’s son should not have been chewing gum at the wedding.
From Emily Post’s Etiquette Daily.