>P.S. - is the term "совок" offensive and derogatory, or it's okay to use?

As has been said above, it depends on the political position of the listener. In general, by the level of offensiveness it is somewhere between 'Murrica' and 'Jewnited States' in the USA =)
P.S. ... of course, if we mean "совок" as a phenomenon, not a man. It is always an insult regarding the person.