what do I type?
I read it was a command...

It isnt a command, just its hardest...

what do you mean?

You dont need an command to do an self dm.
You only need to grab and puch on you with power.

You may set the dismemberthreshold, go to gamerules and edit it to ~20.
Lower numbers = easy dm

I didnt mean that, I meant like in leilaks replays he always get bruised with his own bodyparts,
I mean like self damage

Pabblopic: Go to Game Rules>Damage> Put it as 1.

yea, just figured it out thanks bro.

The actual command to enable self-damage is /set damage 1.