Most Irritating pens to work on?

[top pen]

I just have been working on a Parker 51 Dove Grey that I swear someone must have used India ink in. It took the 5 days of soaking, warming and cooling to remove hood. I think it will take another day to remove the remainder of the gunk in the pen. I now have several blisters on my fingers.

I was wondering what pens other's had found challenging to the point where they wanted to sling the pen as far as the eye could see.