I forgot you Exist
This is when someone says this to feel important, even though they know the other person is still here, probably hates them, and they're still left with the same stupid problem they had before.
'I forgot you exist?' Like you're not still here?
You forgot I exist? I guess you're still mad you didn’t get the last pizza slice.
I forgot you exist? I guess you're still mad I didn't ask you to my party.