"HiHiByeBye".

According to Kugou Music query, we learned that "Say byebye" comes from the song: "HiHiByeBye". Release date: 2008-02-29, from the album: "RedCyndi2008". Singer: Cyndi Wang. Lyricist: Lindbergh, composer: Edry Kru, arranger: MacChew. Excerpts from the lyrics: I say hihi to you, you say byebye to me, we may seem strange, but we have a tacit understanding all the time, I say byebye to you, you say hihi to me, you say it’s strange or not, we get even weirder when we see something strange.