This is potentially referring to two Vocaloid songs:
O-kotowarishimasu is a song by Satsuki-ga-Tenkomori, utilising Hatsune Miku. The song has the English title of "NO THANK YOU" in the video and "No Thank You" is the name of its most popular Youtube distribution. The song is also usually distributed in English as "I Refuse".
The singer of the song is an office worker who is sick of their life. The daily routine of taking the train and heading to work leaves them feeling unfulfilled, and various small misfortunes cause them to feel like giving up. They are plagued by various small grievances, such as traffic jams, spilled drinks and bad hair days. In the end though, to each of these things, they say a hearty "O-kotowarishimasu! (I'm afraid I must refuse!)" "Danko! ([I] firmly [refuse]!)" and "Go-enryoshimasu! (I'm afraid I must refrain!)"
No Thank You
No Thank You is a song by Meiyokaichou-P, utilising Kagamine Len. The song is characterised by the way it pushes Len's vocal to the top of its range.
During the song, Len refuses (ironically) to sing for his producer. He initially says that this is because he is picky about the work he chooses, though quietly reveals it is because of low confidence in his ability, not that he'll admit it. He mentions he was known as DQN Len-kyun (in regards to his rude attitude), and says that in return for this incident he will take all of the producer's unpublished works and post it online. Later, Len recalls that when the producer threatened to return his product if he did not sing, he responded that he does not sing because the producer does not give him enough snacks. Len also threatens to send the producer themselves back, saying he will send him in a box to Hokkaido from Tokyo Bay, telling them to come back as a "splendid Vocaloid".