I'm 27 and single and blow all my miles on fun personal long weekend benders.
I just got back from a weekend in Iceland (KEF) Delta begins flying there next month. Don't stay for more than 3 days. Friday and Saturday do the nightlife and Sunday do the Blue Lagoon to cure your hangover! (Iceland is very expensive once you're there)
Check out Buenos Aires (EZE). Flights there are all red eyes so you don't blow the day flying. BsAs has an awesome nightlife, great food, good looking population IMHO, favorable exchange rate to get more bang for your buck. If you don't speak Spanish it is still easy to get around.
There is always Rio de Janeiro (GIG). Great nightlife, a bit more expensive, the exchange rate has become less favorable.
Last suggestion is Bangkok (BKK). Check out Koh Samui, etc.