This achievement is missable.
You can unlock this during the main quest Dead Man's Party.
Once you have finished talking to the newlyweds with Shani, you may begin taking part in the festivities. There are a total of 10 events at the wedding. Each is marked on your mini-map, so you shouldn't have any trouble finding them. For this achievement, you must complete all 10. After completing 3 events, Geralt (Vlodimir) will take Shani into the barn to dance and Gaunter O'Dimm will arrive. Do not talk to him until you have completed all other events.
This achievement does not unlock until you have finished the quest.