Well Herr Doctor, now I have been made aware that you have a PHD (see 'school reviews'), but are not a native speaker, (refugee was it ? or economic migrant?. It matters little) I can see how the subtlties of the English language continue to elude you.

However just so that you know, the word 'ain't' is perfectly acceptable when quoting well known idioms such as "If it ain't broke, don't fix it" (see The Cambridge Dictionary of American Idioms) so "It sure ain't your work" fits nicely into this category, and if it don't ? "it ain't worth argueing about." (another one there, did you notice ?)

Please continue to entertain with your pearls of wisdom, (I believe sarcasm has been mentioned by another of your fans in the past) we Brits love a verbal joust.

G'day. (beware the wrath of the Aussies)