Guy has followed an improbable path from its origin as an eponym for Guy Fawkes to its common and versatile use today. It’s increasingly popular as a term to address mixed-gender and all-female groups, but not everyone welcomes this development (see video below). So how gender-neutral is guys, you guys?
Instead of a simple answer there’s a spectrum that depends heavily on context. But we can draw some general conclusions, as I did in an article at Slate’s Lexicon Valley on guy(s) as a gender-neutral word:
Addresses like Hey guys or just Guys are widely felt to be gender-neutral; set phrases like good guys are less so; usages like those guys shift even more subtly male-ward; singular a guy and the guy are markedly male. Then we have the likes of a guy thing and guys and dolls, which explicitly contrast guys to the female gender (and belie the fact that many people identify as neither).
Even among the more male uses of guy – singular rather than plural, and in reference rather than address – change is occurring. My article shares intriguing examples of this shift, from both children and adults, then ponders the future of gender-neutral guy(s).
Guy is absent from Casey Miller and Kate Swift’s Words and Women, their Handbook of Non-Sexist Writing (except for a passing mention that it’s ‘being debated’), and Jane Mills’s Womanwords: perhaps strangely so, given its profile. In 1980 George Jochnowitz called the shift in the use of guys ‘extraordinary’ and later described it as ‘the only major change in the pronominal system of English . . . since the loss of thou and thee four centuries ago’ (h/t Manu Saunders).
The ‘American’ uses of guys and you guys are prevalent in Ireland but must compete with other options. Irish English lads has a similar pattern to guys, often used to address mixed groups. (There’s also Ah lads as an expression of general discombobulation.) And of course we have ye, youse, yiz and the like. But guys is holding its own.