title_body: What gives "diner" coffee its distinctive taste?
upvoted_answer: I think it is a combination of old stale grounds sitting on a burner for long hours. The places you mention are generally open 24/7 or something close to it and have people ordering coffee at all times of day, so it's all made ahead of time and kept warm all day.
  
  The cheapest coffee suppliers usually mix beans from all over the place and they all store them way past any freshness date. Diners run on small budgets and generally buy the cheapest stuff, thus they all have the same "flavor".
  
  That combination is not just a diner thing, I would also say it is the same as cheap gas station coffee in the US.
  
  I would knock it more if it didn't keep me awake behind the wheel more than a few times.