The act of unintentionally (or intentionally) insulting yourself.
1) It can happen when your all out of insults.
2) It can happen if you just wanna fml and/or bitch about your life.
3) It can be used in both verb and noun forms.
- Man, I hate you, you keep insulting me like a homo.
- Really? Aren't you gay yourself?
- I hate myself, I hate my job, my life, my parents. You know how stupid I was to confess to her? I failed miserably and went on depression and all. I'm a fucking loser.
- That's crazy... You should stop selfdissing yourself.
3) I am selfdissing because I am worthless.
Selfdiss is the art of insulting yourself.