Dunno about tattooed girls being 'easy'...
The sensation is hard to describe. And as Thatch said, it varies from person to person, and also by location. Areas that have bones close to the skin or have lots of nerve endings tend to be more painful.
Ever been scratched by a cat (or a person)? The sensation is similar, but it doesn't STOP - getting scratched is over quick, whereas the tattoo needle keeps going, and it travels SLOWLY.
I'd recommend that you breathe slow and deep, focus on accepting the sensation instead of tensing up against it -- if you meditate try and do that... when my color work was being done I dropped into a trance from the breathing exercises I was doing, and actually felt BETTER after than before. The line work was when it was new to me, and that's where I tensed up and it hurt.
(dammit, now I want more inkwork. Badly. We're talking a thousand-dollar job too.... unf. I don't have the $$ to actually go thru with it.)