When you are in Belgium and you are staying near the coast then you definitely should go for an evening walk at the beach. After that, you might stop at one of the many cafes/pubs along the dike where you can relax and drink something for the remainder of the evening.
In Belgium you'll find quite some dance clubs for everybody who likes hip hop and dance music. You have to be 16 years old to enter these clubs. Usually, week-ends parties start in a lounge area where locals grab a bite, have some drinks,as a kind of warming-up.. then they head to the clubs they fancy. Dressing doesn't need to be exclusive, mostly just common clothes are satisfactory. Only in some exclusive bars they have a dressing code.