I've never claimed to be an expert. I know my limitations.
However, I can assure you the word, snidiest is commonly used in the Glasgow area, especially when discussing a certain type of person. e.g
Holding made one of the snidiest remarks, I have ever heard.
I hope you are not showing discriminating towards we Scots. If so, I shall be forced to report this. 
Nemo me impune lacessit. ?