As you all know I am a atheist and I am on an extended long term trip in the Caribbean training ...?

If you are a scuba diving ual atheist why do you care about what others think about your friend cracking a joke about christians? I think I must be missing something, by the way I do not know what caribbean island you are in, but I do know that diving is really good in St. Lucia and Barbados (just in case you have not been to these islands)