Originally Peter Mullan planned to shoot the film in the same style as Ken Loach - ie, shooting in sequence and only giving the actors the scenes that they were required to do on the day so that they wouldn't know the outcome. However, Mullan only caused greater problems for himself by not shooting in sequence as he found himself constantly explaining to the actors what they had just done chronologically. After two weeks, he relented and gave all the actors the full script to read and learn.
The film uses "Non-Educated DelinquentS" as a "backronym" for "neds" as it is commonly used in modern day Scotland since the 90s. The English equivalent is chav. Many people including police officials and politicians (including famously Rosie Kane MSP) have discussed the term ned using this definition. As the term ned has been used far longer and dates back to the 19th century according to the OED it is not proven that this is the true origin of the term.
It is widely believed the term NED to be an acronym for Non Educated Delinquent. This is inaccurate and came about mostly due to its use by a Scottish MP in the early 2000s, it's use today is rather a backronym with the term NED dating back to the depression in Glasgow in the 1930s alongside Teddy Boys. It is now more accurately thought to have been derived from Edwardian because of the fashion at the time of the many Glaswegian street gangs.
The main character on the edge of sanity has a weapon in his hand and play-acts tough guy in front his bedroom mirror similar to the famous "are you looking at me" scene with Travis Bickle.