The misleading idea today is that missionaries are those who work with a christian organization in a foreign country.
The error could be further from the truth. The idea of being a missionary, is to preach the Gospel to non-believers in the most active means not seen in other offices of ministries. It can be supported by a church, not supported by a church, if the primary goal of a missionary is not achieved, one either cannot be a missionary or that one is a failed missionary.
So when someone say to me they are missionaries or are missionary kids, unwittingly I would have to first wonder...because I might not have to take them as seriously as I take a true missionary. I would talk to them about: - So how's your "vacation" in foreign land like? What do you love to eat there most? Do you like the sunsets there? And they wouldn't be offended, I'm sure of it.