I hear many people these days on TV and radio using "themself." So why are they using it and what are they trying to communicate? Let's think about it logically. "Self" refers to one person. When you're using "them," you're talking about multiple people, not just one person. Some people are using the term "themself" as a way to get around unknown gender without having to say a mouthful like "himself or herself." However, "themself" is not correct.
For example, someone might say, "A person can find themself in a precarious situation very quickly."
The grammatically correct way to say this is, "A person can find himself or herself in a precarious situation very quickly."
Also, "hisself" is not correct. I have heard this one many times too. I think this is really just a result of lazy speech. Swallowing that "m" is somewhat easier. However, it is not a word.
Introduction to Grammar Guidelines
With texting, Facebook, and Twitter fast becoming main modes of communication, the new shorthand lingo that is developing will no doubt bring about a higher frequency of grammatical, spelling, and punctuation errors. The rules that define proper English seem to fade into the distance as more people forget them and replace that knowledge with acronyms such as OMG and LOL. The hope for this site is to reinforce proper English grammar and continue to encourage eloquent writing and speech.