Grammar

I read two interesting articles about grammar at Mental Floss.
I found these things to be of note:

• ain't is a contraction of am not (as is "amn't") and is proper English
• double negatives are perfectly okay in English (making "ain't not" proper as well)
• sentences can be started be can started with a conjunction
• sentences can be ended with a preposition

And I ain't not surprised by this (…at).