In her appearance on Between Two Ferns with Zach Galifianakis the funny comes from how "Zach" is damping down his normal tendency to be antagonistic towards his guests because he's obviously very attracted to (and somewhat intimidated by) "Charlize", but at the same time, he can't help being needled by her immensely patronising compliments on how funny he is. It all culminates in this:
Charlize: [to camera] Donít put this on camera. [leans over to Zach, whispers] My thighs are so sweaty right now, itís like, dripping all the way down to the back of my knees. Look at this. Itís like, the only thing that could cool me off right now is to jump naked into a pool, itís so fuckiní hot.
Zach: Are...are you asking me to go with you?
Charlize: [stares at him blankly] Where.
Zach: ...In the naked pool.
[Pause. Charlize cracks up laughing. Zach is not amused.]
Charlize: Oh my GOD! You are HILARIOUS!
Zach: [muttering] I wasnít joking.
Charlize: You know how you made it really funny, is because the image, of, like, me and you, like, me, naked, in a pool, with a fat garden gnome, like ... [cracks up laughing again] Thatís like really good! You are really good. You are really good.
Zach: [profoundly humiliated and angry] ...I hope your dog dies.
Charlize: [cracks up laughing again] ...I just pissed myself.