You can say
'who is she kidding?
' or 'who is he trying to kid?
' if you think
it is obvious
that someone is not being sincere
and does not mean what they say.
She played the role of a meek, innocent, shy girl. I don't know who she was trying
'Maybe tomorrow will be better,' I said, hanging up. 'Who am I kidding?' I told Wolfe.
'Tomorrow will be more of the same.'
COBUILD Advanced English Dictionary. Copyright © HarperCollins Publishers