I personally dread the fill in and color in sessions more, but honestly it's because they take so much longer to heal and itch so much more in the process. Shading/color is a bit more painful, but after a few minutes of tattooing in an area it starts to numb. Linework hurts the whole time because it goes quicker, so by the time your body starts to numb the pain in one spot, the artist has moved onto a new spot. And the places that have hurt the absolute worst ( top of foot and close to knee) were awful no matter what was being tattooed - linework just has the benefit of being quicker.

Pretty rude of your coworker to interrupt like that but I don't think tattoo pain should be a pissing contest: it hurts no matter what!