I think I have got this right, Quizmonster (or monger, I forget) will know, but words like whelmed and kemped (as in unkempt) used to mean something, but while the original word got dropped the modified version remains. I don't know why. I'm probably wrong now. I'll post this anyway just so that somebody can have the pleasure of correcting me.
I have seen that film, but not recently so I don't remember the line. I must have subconsciously ferreted it in the back of my brain! I often think the same thing about uncouth - can you be couth?