It depends on your personal situation. If you have the luxury of ID travel, with 4 days the world is literally your oyster.
London is a cinch at this time of the year.....flights wide open both outward and return. You might even get some good weather.....and if you like Tennis, Stella Artois is on. Paris is slightly harder from BAH, with only 4 flights per week (IIRC) but they should be pretty empty this time of year as well.
Alternatively, if you don't fancy Europe, ehen you're in the Gulf it's an ideal time to visit the subcontinent, if only for the experience. And with a 3-4 hour flying time you would maximise your time on the ground.
Failing that just head down to Dubai!
(Oh, and based on a recent experience, 3.5 days is just enough time to 'do' Hong Kong.....)