What are other gods?
Are they not the result, at the other extreme, of the idea that there is something else besides the Holy One, Blessed be He?
Of course, this is at the extreme end, while at close range, we have the miniature idolatry, when a person worships himself.
To be sure, it depends on the situation; sometimes it is quite emphatically avodah zarah (idolatry) and there are people for whom the self is the only deity whose authority they are willing to accept.
As the Sages have said, anyone who is proud is like one who worships idols, the common factor being the acknowledgment of one's self as primary.
Also, a person who surrenders to anger or any passion is like one who indulges in a sacrificial rite to himself.
–Rabbi Adin Steinsaltz
From In the Beginning, "The Many Sides of Chesed," by Rabbi Adin Steinsaltz