"If I were you, I'd know they was joking"

No, alright, the title is just a joke, but I have a very simple question which pains me even more, because even despite its simplicity I am having second thoughts. It has to do with the pronoun "they" being used to refer to a single person. After consulting with my fellow linguist Mr. Google I found out that the reflexive singular for "they" being "themself" is, in fact, a real word, and can be used. And that made me increasingly paranoid towards using "were" form of "to be" with "they", while: *"They were eating an apple."* sound absolutely perfect, the fact that "were" is referring to a single person is a bit jarring. But on the other hand reading: *"They was eating an apple."* makes me regret ever being literate, even though for some reason my sub-consciousness likes using "was" when referring to just one person. Seeing how "were" may actually be used with a singular pronoun as shown in the title, I am heavily leaning towards the first variant, however I just felt obligated to ask because I am curious like that and all.