two girls fight over the phone. Apparently, the other end asks: who are you?
this end says: "I'm your worst nightmare is who I is!"
for the second is in the sentence, i think that am is what should be there. why is IS here?


Your worst nightmare is what I am.

I'm your worst nightmare. That's what I am.

The original is simply awful.
Occasionally, educated people use bad grammar to play with language a little, to amuse themselves or others.
This would commonly be with friends in an informal situation.

Do they ever do this in your native language?

Best wishes, Clive
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Incorrect grammar I would assume? O_o
It definitely should be "I'm your worst nightmare is who I am!"
Though even in that form, the sentence seems too colloquial to me ><
"I'm your worst nightmare, that's who I am!" hurts my eyes less....
Who am is?
you got me confused.
but i think it should be who I am.
but am not editor either am I a writer so,
I guess whatever fits you.
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