Here's something to do at night... Go and party till the early hours of the morning! The most popular clubs in Bahrain right now are BJ's and Savage Garden... They're definately packed on weekends, and on some weekdays too... There are also significant others such as the Key club etc, and these usually play western music...
There are also many arabic nightclubs, which can be fun too, though they are not as openly popular as the previous...
Some nightclubs won't let you in without membership, some only couples, while most other take an enterance fee... They usually are worth it especially if you like to dance and let it all go for the night!