Theirself vs. Themself: What's the Difference?
Theirself and Themself Definitions
(reflexive pronoun) The reflexive form of they, the third-person singular personal pronoun. The single person previously mentioned, as the object of a verb or following a preposition also used for emphasis.
Someone could hurt themself.
Anyone who wants a car like mine can buy one themself.
Synonym of themselves.