We even have a restaurant called Rymy-Eetu in Helsinki. It's a place where you can have fun.

rymy, and its derivitaves ryminä, rymytä, rymyjuhlat, jne. denote noisy and boisterous conduct, or it could be applied to an energetic animal, as in http://geocities.com/hopperskennel/barre.html referring to a dog "Oikea rymyäjä, jokaisessa kuralätäkössä on pompittava ja elämästä on otettava ilo irti Barren mielestä".

Just a suggestion. I read the biography of Bon Scott (AC/DC) a while ago and he was frequently described as being mischievous. He was definitely a 'rymyäjä', there's no doubt about it :) Rymyäjä can also be used when talking about kids as stated above.