I have been to Negril more than 40 times last time being in 2012 and have never ever heard about any dress codes to be followed except as some have suggested, in AI Dining Rooms or a High End restaurant. That is what is so cool about Negril is that everybody is accepted despite their looks, color, creed, etc.... many places that were around long ago (The Wharf Club Restaurant, Negril Yacht Club, Pee Wee's, etc...) were pretty much swim trucks / shorts, bikini's T-shirts, whatever works. The only thing I can remember was that the Jamaicans (Negril locals) were not keen on nude sunbathing on their property but nowadays I guess that depends on where you stay and what the hotel rules are. Water shoes are helpful as there are sea urchins and sharp coral in some places that can cut your feet pretty bad. Giving clothes to less fortunate Jamaicans before you leave JA can forge a friendship to last a lifetime!!!
We booked our next trip within a month after we got home. Once you go, you know! 
