Good: "regex", "func". Bad: "regexp", "fn".
This is because I hear code aloud in my head when I read it, and if I don't know how to pronounce something it interrupts my reading momentum until I figure out some way to say it.
Naturally I suppress my reaction because it's just a coding style thing and not worth arguing about with colleagues and collaborators.
But it is definitely a strong enough effect that if other people had my tendency we would never get a keyword like 'fn', at least from other native English speakers. The explanation I've tended to believe is that other people perceive code more visually and less audially than I do.