What idiom should be used to define the situation of a person's life when he/she knowingly harm himself/herself?

Tapas MandalWhat idiom should be used to define the situation of a person's life when he/she knowingly harm himself/herself? Like 'hitting someone's leg with his own axe'? But I don't know whether it would be suitable to define such situation.

Does he harm himself/herself,or others?

Yoong LiatDoes he harm himself/herself,or others?

Obviously when "he harms himself".

What idiom should be used to define the situation of a person's life when he/she knowingly harm himself/herself?
Like 'hitting someone's leg with his own axe'.

The two bold parts seem to contradict, especially with "someone's leg". In my opinion, it would have been better if you had written: Like a person hitting himself with an axe.

Thank you Yoong for apprehending. But that does not give my answer.
I want an appropriate Idiom/synonym for the same.

Thanks in advance.

A poor man whom I knew nursed the orphan. (A good ,man nursed the orphan. I knew him.)

I know the poor man who nursed the orphan. (I know the poor man. He nursed the orphan.)

Subject -- who
Object - whom

him ends with m: whom also ends with m. (This is the way I remember when to use who and when whom.)

Hello, moderator,

Please delete the above post. It was wrongly posted.

Thanks.

Yoong.

Tapas MandalThank you Yoong for apprehending. But that does not give my answer.I want an appropriate Idiom/synonym for the same.Thanks in advance.

I would use the word "masochistic".

The most appropriate idiom that I use for conveying such a meaning is - 'Digging your own grave'.

E.g. I dug my own grave when I invited my ex to my birthday-party!