= Kono atsusa de kanari kiterune.
= This heat really got her. (This heat made her crazy.)
キテる ＆ イっちゃってる ( = kietru & icchatteru)
キテる = kiteru
is originally a verb 来る ( =kuru ) →来てる ( =kiteru)
It means to reach to certain point or degree and it has both negative and positive meaning.
★Positive meaning :
→getting very popular, great
We use it often to describe someone such as musician, models, actors who are about to be very popular. You can also use it for things like games, software or music.
= Kare (Kanojo) kiterune.
= He (She) is becoming very popular.
= Ima kono kyoku kiterune.
= This song is getting to be very popular (now).
→going crazy, going nuts
It related to this idiom.
= atama ni kuru
It means “to get angry” and also “go crazy“
So if someone says
= Chotto atama ni kita mitaine.
It could mean someone is either angry or going crazy.
キテる is on the brink of ヤバい ( =yabai!) to be in a bad mental or physical condition
= (atama ga) ikareteru=be crazy
= (atama ga) yarareta
= Maggie sensei ikarechattanja nai?
= Atama yararechattanja nai?
= Isn’t Maggie-Sensei going crazy?
We also use this to malfunctioned machine.
= Konpyuutaa ga ikarete shimatta.
= My computer went haywire.
•イっちゃってる ( = icchatteru)
It came from a verb 行く( =iku ) = 行っちゃってる ( = icchatteru)
It’s literal meaning is “one’s soul or one’s mind is gone to another world which is far away from our normal one”
So we use it for someone who is crazy, spaced-out, kooky, nuts, wacko.
We also use it to describe someone who is overly absorbed in something.
= Anoko chotto icchatteru ne.
= Me ga icchatteru.
= One’s eyes look crazy.
Note : The spelling キテる+イっちゃってる ( = kiteru + icchatteru) could be written きてる、キテル、イッチャッてる ,etc.
There is no specific rule but we tend to mix hiragana and katakana to write slang.
=Dare? Watashi ga icchatterutte itta no wa?
=Who said I was going crazy?!