It can also be "parts of a person's character" or "propensity" :

e.g. He seems to have a propensity for lying all the time.

"someone’s middle name" is another suitable answer:

e.g. Lying and lying, this is always his middle name.

Or if you want to mention that someone will never change their behaviour or character, you can use"a leopard can’t change its spots":

e.g. A: Don't trust her - she's lying again. B: I know, a leopard can’t change its spots!

Apart from second nature that our friends have pointed out It can also be "parts of a person's character" or "propensity" :

e.g. He seems to have a propensity for lying all the time.

"someone’s middle name" is another suitable answer:

e.g. Lying and lying, this is always his middle name.

Or if you want to mention that someone will never change their behaviour or character, you can use"a leopard can’t change its spots":

e.g. A: Don't trust her - she's lying again. B: I know, a leopard can’t change its spots!