I find myself often winging it with “themself/themselves” and it seems to be like themselves is always colloquially correct when there are multiple preceding nouns you’re referring to…
Otherwise if there’s only one antecedent or whatever, its themself
Be gentle haha
Weird - I never noticed that the third person reflexive forms typically use the main case (him/them) as a basis, while the others use the possessive (my/thy/your/our). No idea on why this difference.
That said “hisself”, “theirself” and “theirselves” don’t sound bad to my ears.
It also doesn’t help that the third person feminine is ambiguous. There’s often no distinction between the accusative “her” and the possessive “her” (except when the pronoun appears in a different part of the sentence and becomes “hers” - fuck I hate English), so it could be interpreted as fitting either rule.