For a small Swiss town, Interlaken has quite a lot of nightlife options, including one of Switzerland's three Hooters Bar & Restaurant. Most of these bars serve the seasonal tide of tourists, but off the main road, many more mellow local venues can be found. Try the Brasserie 17 Rosenstr. 17 which has a nice summer terrace,good beer and snacks and sometimes live music.
The two best nightlife spots in town are Balmer's hostel and the Funny Farm, which are located fairly close to each other both at Hauptstrasse, Matten. Balmers has a decent underground bar and dance club and the Funny Farm has great outdoor chill out areas, including a bonfire. Both hostels have good happy hour specials, and you can kind of bounce back and forth between the two to get your drink for the best price.
Rugenbrau 'lager hell': the local beer is OK. The water in the area is the cleanest in Europe. Drink that instead. You won't be disappointed in its cleanliness.
