I've carried around a note of my all-time pet peeves in technical writing, and kept them to myself at least since 2008. One of them is, to quote myself:
Write for the target reader who doesn't know anything, so you can reuse the same first ten know-nothing chapters in all your books.
So I cringed when I read in Exercise 4
Note: The _ in space_in_a_car is called an underscore character. Find out how to type it if you do not.
Patrick: I'll never learn Python, I can't find the underscore key!
Spongebob: Why don't you find out on Google, Patrick?
Squidward (derisively): That's spelled G-O-O-G-L-E!
(one hour later)
Patrick: I can't find the G key!