Flow chart: when to use “guys” and when to use…all the other terms. Definitely worth enlarging.
Specifically regarding the use of ‘guys’ — this flowchart, you’ll notice, only has you use ‘guys’ for all-male groups. Now, this flowchart is intended to be prescriptivist (like, obviously; it’s trying to tell you what words to use) and that’s fine in this instance, seeing as it deals with Gender Identity Things and Sexism Things and Respect For People Things. But it’s worth pointing out that at least where I live, this rule is FAR out of line with usage. At least where I live, all genders of people use ‘guys’ for all genders of groups, to the extreme of a female thus describing an all-female group. Of the few non-binary-identifying people I know irl, one specifically says that they consider ‘guys’ a gender-neutral term. (I do not know the others’ opinions.)
But we’re free to decide that we don’t want ‘guys’ to be a gender-neutral term. So the question remains, do we? In my mind: 1. It’s good to have gender-neutral terms; as the above flowchart shows, gender-neutral names for groups are a thing we need; ‘guys’ (at least where I live) is becoming a better and better candidate. On the other hand 2. It’s very unfortunate that it’s always the male term which becomes the gender-neutral term. (actor/actress, hero/heroine, gay/lesbian, etc — the first term can be either specifically male or much more general, right down to ‘Man’ encompassing all of Humanity. Read Hofstadter’s essay about this!)
This is hardly my choice to make, but for what it’s worth that’s how I see the pros and cons.
As far as I’m aware, this flowchart was made by 1 or 2 people (see credits at top) talking to each other about how they would use this set of terms and what they would interpret other people to mean when they used them. So dialect differences are very probably to be expected here.
Like several commenters, I also have “guys” as a gender-neutral term but only in certain contexts.
So I can say “What are you guys doing?” and I could be talking to any plural group, but if I say “When will the guys leave?” that refers to a group of males. (On the other hand, “where are those guys going?” is gender-unspecified again, at least for me.)