Hardest Instrument To Play

Sitar is hardest because of Indian Classical music theory. Depending on the weather, time of day, season, you play in a different key.
 
I don't know about all the foreign instruments but out of the ones I know I would say drums because you have coordinate both your hands and both your feet which is pretty damn hard (at least for me)
 
It depends on what drumming your doing. If you're doing some Hip-Hop drumming it would be pretty damn hard. A lot is electronically made because it would be way too hard to play manually.