It is set in episode 27.
Kagamine Twins: Oh, screw you...
Overlord: You must become evil.
Kagamine Twins: We'd had enough of being evil! That was so long ago!
(The Kagamine Twins get the road roller, crush the Overlord, and put it aside. Then they retrieve Cole and Jay and use their Spinjitzu to bring them back to normal.)
Cole: That girl will be my girlfriend!
Jay: I thought you liked this girlfriend!
Gumi: You mean Gumi, thank you very much.
Cole: That's gumi? I thought that was Gumi! (points at Rin Kagamine)
(The Kagamine Twins do the same with the evil people of Ninjago, as called by Teto. When they turn good they dance to Only My Rail Gun.)
And episode 27 continues.