The fuck's wrong with saying y'all? It fills a hole that's missing in the wider English language's pronouns.
Singular first person: I
Singular second person: you
singular third person: he/she
Plural first person: we
Plural second person: ( )
Plural third person: they
English is also missing a non gender-specific third person singular pronoun, which is used when you're trying to specify a hypothetical person who you don't know the gender of. For example: "If a person jumps, he/she falls to the ground."
For now, I believe that to be grammatically correct, 'he' is technically used as a placeholder, since male pronouns are supposed to be the default when gender is unknown. Another option is using 'they' as both the nongender singular and plural third person pronoun. Both options are slightly awkward, however.
Other languages don't have these two gaps in their pronouns. For example, the Spanish y'all is 'vosotros,' and the nongender singular pronoun is 'usted.'