Here is a kind of answer from a student of ancient Greek (me!). You can say that it is a kind of abbreviation (from 'unfriendly user'). So it involves ellipsis (leaving something out, which has to be 'understood' by the reader/hearer. It looks, as it stands, somewhat germanic, and I am tempted to say that it should therefore be written as a single word ('userunfriendly'). But that violates an embedded sense of how things should look (and sound) in English. As I have left it, the word 'user' functions as what in logic is called a 'predicate modifier' (something that changes the meaning of a predicate {adjective}). This is interesting, because, whereas in the past these things would eventually be settled by the emergence of authoritative dictionaries/grammars by specialists giving names to phenomena such as this, this is no longer how it happens.