The word "機歪" (simplified Chinese: 叽歪), means that a person talks too much (probably complaining about something) so that it annoys people around him/her. This is not a formal word that you could find out in a dictionary, and more like a word from spoken language. Besides, another word often used in spoken language is 機機歪歪 (simplified Chinese: 叽叽歪歪) has a similar meaning. 

"固執" and "任性" have different meanings. "固執" means stubborn, while "任性" means capricious. 

In the song, "固執任性機歪" means 固執，任性，and 機歪.