Mittaphab Club and KTV is the nightclub of the Mekong Hotel on Souphanouvong Avenue. It is about 500 meters from the tourist center.
I saw it as I was walking by and I decided to have a quick look. The entrance was free and I just had one beer (25,000 kip).
It is a rather large disco but less than 50 clients were there. It is a bit old-fashioned: You have a podium for the live band, a dance floor just in front of it, and used sofas all around.
The music was Laotian. The male customers were above 50, maybe Chinese, but most girls were in their early 20s (except a few older ladies). I presume they were hostesses from the karaoke next door.
Depending on the song, they would all start to dance, sometimes in groups as you can see on this video I took inside:
Overall: Unless you are a Lao citizen over 50, I don't see any reason to visit this place.
Mittaphab Club et KTV (also spelled Mittapharb and Mittapharp)
Souphanouvong Road Vientiane
Open every day until 12AM