Sarcasm is essentially unused and unrecognized.
Patois is the local language and most commonly spoken everywhere except Castries . As a tourist you may be regularly addressed in English but expect St. Lucians to speak amongst themselves in Patois.
St. Lucians are known to be quite friendly. Expect to say hello and strike up conversations with strangers. Expect them also to not adhere to the racial sensitivities many areas are accustomed to, which is not intended to be offensive (think “hey white man/woman”) but curious.