According to the timeline of holidays in the Campaign Setting, there is a holiday called 'Jestercap' celebrated in Druma, Taldor and Andoran on Lamashan 27. Is is there any information elsewhere on what this holiday or festival might be?
It's not mentioned in the entries for those countries ... or maybe it is and I just missed it ...
I checked the Taldor Companion and there's no mention of it there, either. Maybe when the Andoran Companion is out it'll tell us about it. :)