Appending 'Schmain' to 'Pain' indicates complete nonchalance on the behalf of the utterer with regard to the promised, expected or forthcoming pain.
The idea being expressed is that Pain will affect him no more than Schmain would. There is no such thing as Schmain.
Macduff: You are entering a world of pain, boy.
Macbeth: Pain Schmain.
The jewish way of saying "hurting"
Mostletoff!! Fuck that Pain schmain