To be terrible at something

[alpacinoutd]

Hello.

I want to say I'm really terrible at something or I can't do it. Can I use "can't do...to save my life"? How common is it? Do people actually say it?

Have I used it correctly and naturally in these sentences?
1. I can't wake up early to save my life.
2. I can't swim to save my life.
3. I can't learn grammar to save my life
4. I was very shy when I was in school. I couldn't make friends to save my life.
5. I really hate Indian food. I can't eat Indian food to save my life.
6. When I was in school, I couldn't cheat in exams to save my life.

[Tdol]

It's fine to use it like that. I wouldn't say that is particularly common, possibly because we have many ways to express the idea.

[tedmc]

I think this other phrase is more common, and means the same thing:

For the life of me, ...

[Charlie Bernstein]

I think this other phrase is more common, to mean the same thing:

For the life of me, ...

They're both common but have slightly different uses, which can overlap.

We usually use to save my life the way Al did: To express total inability to do something ever.

We usually use for the life of me for more immediate problems, often involving forgetfulness:

- I can't remember her phone number for the life of me.

- For the life of me, I don't know where I put that recipe.

But you're right, they're interchangeable.

[Piscean]

I think this other phrase is more common, and means the same thing:

Typo.