Self-deception can be divided into at least two types:
1) Deluding yourself into thinking that you are better than the median in some particular trait, like driving ability, teaching ability, and etc.
2) Deluding yourself into thinking that the traits you just happen to be good at are considered objectively more virtuous. In this form of self-delusion, you do not actually think of yourself as better or worse at any particular trait, but rather rationalize traits you are good at as especially virtuous, and traits you aren't good at as especially useless or even evil. As Michael Vassar explains, people "delude themselves about what traits a human without specific information about his or her self sees as good, choosing to see many of their own traits as good rather than as bad and failing to notice that people who lack those traits consistently see things otherwise."
If you tested them, I'd bet that people will be more likely to self-deceive using type #1 self-deception for traits about which they cannot plausibly self-deceive using type #2 self-deception. For example, almost everyone in our society agrees that getting along well with others is a virtuous trait, and it would be relatively difficult to come up with a plausible argument otherwise. So, it makes sense that in one study (see pg 11 here), when asked how well they get along with others, all students thought they were above average, 60% thought they were in the top 10%, and 25% thought they were in the top 1%.
In the modern world type #2 self-deception has become especially common due to the desire to find one's own niche. Given arbitrary weights of values for traits and their interactions anyone can delude themselves into believing that they are the most virtuous person in the world.* This also helps explain some of the benefits for being part of an "in" group, as your group will validate your type #2 self-deception about what makes a virtuous person.
* This is provable via Arrow's impossibility theorem.
