Wow hands down the one where SJ is dressed up like vegetables and well..just watch the video! I promise you will die laughing! :) It's not really a performance I just find this funny. :)

http://www.youtube.com/watch?v=oOrY7ahYzl4

Then I guess my favorite kpop performance would be of Super Junior singing "She's Gone"

http://www.youtube.com/watch?v=IG8njT-yFwI