flatter

[Isbell]

I flatter myself that I am the best means I'm glad that I'm having the best quality as compared to the others. I want to check if I'm right in my interpretation.
Thanks.

[Beeesneees]

Not quite.

To flatter yourself generally means to make oneself feel pleased by believing something favorable about oneself, typically something that is unfounded, as in definition number 4 below:

Flatter:
1) Lavish insincere praise and compliments upon (someone), esp. to further one's own interests
she was flattering him to avoid doing what he wanted

2) Give an unrealistically favorable impression of
the portraitist flatters his sitter to the detriment of his art

3) Make (someone) feel honored and pleased
I was very flattered to be given the commission
at least I am flattered that you don't find me boring

4) Make oneself feel pleased by believing something favorable about oneself, typically something that is unfounded
I flatter myself I'm the best dressed man here

5) (of a color or a style of clothing) Make (someone) appear more attractive or to the best advantage
the muted fuchsia shade flattered her pale skin

6) Please (the ear or eye)
the beauty of the stone flattered the young clergyman's eyes
_________________
Cheers m' dears!

[Isbell]

That means if X flatters himself that he has something good about himself, but it really is something that might not be true (and usually it isn't true)?
My guess, was it getting from bad to worse???

[Beeesneees]

NO - it just means he is giving himself more credit than he deserves for something.
_________________
Cheers m' dears!

[Isbell]

Get it this time and thanks a million. As I always tell my relatives/friends, to learn English effectively, you must have "friends" in "high place", of course :)