Is lying a disorder or a skill?

No

Lying itself, particularly lying believably, is a skill. It’s something you can learn, get good at, and perfect to the point that it is a natural action.

The pathology of lying – why you do it -may be a disorder.

Not all lies are equal. Telling your wife “no, you don’t look fat in that dress” is a lie, but it’s a minor, and usually permissible one.

Lying to the IRS or your boss is another thing all together.

@elbanditoroso She is not fat she is undertall.

Careful @RedDeerGuy1, I’m a 6’ 5” woman stuffed into a 5’4” body. I choose to see that comment as being POLITE & NOT as a lie!!!

Now to your Q, I wouldn’t minimize the effect of a liar by calling it a disorder. That gives them an excuse to lie!!! Then again not all liars are driven by any disorder. Some lie for the sake of lying!!! They feel they’ve accomplished something when they get away with lying. Others truly can’t control their lying ways!!! It’s extremely hard to tell the difference so I do my best to cut BOTH kinds out of my life.

undertall = vertically challenged

Excellent answer @LadyMarissa
totally agree.

Lying is a human trait. Only humans lie.

And they aren’t fat, they are gravitationally challenged.

Lying takes skill.
It is a learned behavior. It is a character flaw. Some people lie for survival. Some lie thinking it creates an advantage. Some lie because they can’t stop. Some lie to be hurtful to others.
A good liar practices and hones their skill. Lying requires many skills including managing your emotions, detecting or monitoring how others react, and of course remembering the stories you tell.

Look at politicians – they have perfected their lying skills to the point where people regularly believe them.

Not everyone can be a Nixon, or a Trump, or even a Clinton.

My dog lies to me all the time!

She’s fat. Why is that an insult?