Nachäffen means 'to ape' or 'to mimic' someone, usually in a mocking or childish way. It's a wonderfully descriptive verb, combining Affe (ape/monkey) with the prefix nach- (after), literally meaning "to ape after" someone.
In the song, Namika uses this word to complain about her partner's behavior, singing, "Vor unsern Freunden äffst du mich nach" (In front of our friends, you mimic me). It's a perfect, slightly cheeky word that vividly illustrates her frustration with his immaturity.
Ever felt like you're speaking a completely different language from your partner? Namika totally gets it in her song "Kompliziert." She's laying out all the classic, frustrating moments in a relationship where communication just breaks down. She complains that no matter what she says, he twists her words: "Ich sag' Nein! und du verstehst / Verdrehst den Sinn" [I say 'No!' and you understand / You twist the meaning]. It's a super relatable song about feeling misunderstood by the person who's supposed to know you best.
Namika's solution is both funny and a little bit savage: she tells him it's his lucky day because she has a dictionary for him. The chorus is the perfect summary of her frustration: "Ich bin nicht kompliziert, du verstehst mich nur nicht" [I'm not complicated, you just don't understand me]. She points out how he acts like the "Chef" [boss] in front of their friends but brings her breakfast in bed at home. In the end, she seems to accept him as he is, but she's not going to stop pointing out the problem. It's a fun, clever take on a universal relationship issue.