Just read about this phrase on a blog
‘Allez chercher des poissons dans les arbres!’
It is supposed to be a derisive remark but seems very colourful. Apparently the literal translation is something like ‘Go look for fish in the trees’, so I hope you get the drift!?
Well, if I only I knew how to pronounce it properly then I may get a chance to try it(!) the next time I visit France and am in need of some expressive (but decent, hopefully) French.