Tony -

Makes you promise not to do it again

Steve -

He asks you why you would do such a thing

Clint -

He promises not to tell anyone else

Bruce - 

Is very understanding

Thor - 

Is confused as he is not familiar with it

Loki -

Listens to you rant and explain why

If anyone does self harm, please find someone to talk to about it because it's not something you should have to suffer through on your own