¡No faltaba más!
If you request you for something like. ¿Le importa pasarme la sal? The response is: "No faltaba más, ahora mismo se la pase". Now what does NO FALTABA MÁS means here?, Is it I DONT MIND or something like that?
4 Answers
No faltaba más is also used as an idiom to say 'don't mention it' or 'you're welcome' - but this usage could be regional. 

If someone wants the salt, they will never say "¿Le importa pasarme la sal?" We normally say "Pásame la sal por favor" or something similar.
"No faltaba más, ahora mismo se la pase".
There is something strange with this sentence, aside from the grammatical mistakes.
The common phrase is "Ya no faltaba más" and is used as "That´s all I needed" when feeling fed up or frusted with something.
As Kiwi says, this idiom has more than one meaning. Other meanings are "why of course" and "please do".
I would say " Me pasas la sal por favor ?" and i would say " Claro que si , aqui tienes"