NO, Thank You! is a single by Ho-kago Tea Time, produced by Pony Canyon and published on 4 August 2010 within the album of the same name. The song is the second ending theme of the second season of the anime.
The song was sung by Mio Akiyama's voice actress Yōko Hikasa, written by Shouko Ohmori, composed by Hiroyuki Maezawa and arranged by Shigeo Komori.
(from K-ON! wiki)