If you are just asking for “Scotch” in a bar, you are going to get whatever cheap crap is in the well; probably J&B or Dewers; maybe a really high class bar will have Walker Red Label as their ‘well’ Scotch, which is pretty rough but suitable as a mixer. If you are ordering Scotch or any other liquor ‘neat’, ‘on the rocks’, or in a fine cocktail like a Rob Roy or a Manhattan, then you should specify the label. Ditto for (gin) Martinis and anything else where the flavor of the liquor comes through.
Stranger