I think that one of the film's few mistakes/imperfections was to have used that scene with the incomprehensible dialog be the FIRST speaking that the audience hears. Maybe the director didn't foresee that he'd get such a wide international audience, but then again, the film was entered at Sundance and other North American film festivals, so he should have known that viewers in America and other English-speaking countries would have difficulty understanding a character with not only a decidedly "thick" accent or brogue, but also portraying extreme intoxication by slurring his speech, etc.

A number of the respondants to "viewer reviews" on Netflix complained about difficulty understanding the characters' accents, which shouldn't have been a problem for the main characters (certainly wasn't for me, anyway). I think these folks were alarmed by their inability to make any sense of that first scene's dialog that they immediately turned on the DVD's subtitles without realizing that they wouldn't really neeed them for the rest of the, er, fillum.

The director's commentary with the DVD says "I don't know why people think the heroin addict is The Guy's brother." Well, I know why ~ one of the very few intelligible lines the junky speaks is a question about "how's our Mum?" Or at least that's how it sounds to me...