hmmm...interesting scenerio. I don't really think it's appropriate whether they're strangers or not...unless you know this person well and know that they are joking and they know that you know they are joking.
Appropriate recourse? Well, I get angry and might do something I'd regret because I'd be stooping as low as the person who was a stranger or wasn't joking....I'm might throw a punch or I might (if somewhat calm) isolate the person by telling everyone present what they did thereby making them a social leper. I don't know exactly what's appropriate when I'm mad.