One promise i can never keep!

Slash and cut it what i want.
I've done it so much its hard to stop.
I keep all my promises except this one.
Everybody tells me to stop but all i say is bug off!
The first time you saw them i said the cat had done them.
The second time you saw them i said i made them.
You started to cry and told me to stop. i said i would but i just said it so u would bug off.
i cut my arms and my legs u sometimes see them but you could never understand.