"Joe is the kind of person who would do crossword puzzles in ink."

I would agree with what others have said here meaning that he is self assured and confident and making a mistake is not an option. Me, I would use black ink and colour in some of the white boxes and then give the crossword to someone else to do

It says something about the confidence of the person. That he is so sure of himself and wouldn't think of making mistakes at crossword puzzles. Interesting, considering that the horizontal and vertical lines of the puzzles mean there is a bit of planning involved. If you're the same, then I would also think that you are a very confident individual too!

Yes, I can understand that... I do crossword puzzles in pencil, especially the more difficult ones. I like to write the words in that I think they may be to see if I can any other clues for the other words that cross them. The easier ones in the daily newspapers though, I tend to do in ink. I am fascinated at how my brain seems to have tuned into them over the years, probably because these daily puzzles are written by the same author and it is as if I can read his mind. _Derek

To me, that means that you (and Joe) are well-learned and very confident. To do crossword puzzles in ink means that you don't doubt your choices of answers. People who use pencils exclusively for crossword puzzles have less confidence in their answers and are ready to erase and change their answers. So, congrats for being one of the smart ones!