DDoSing (read before you delete i'm not gonna ddos anyone)

Do you think that it is right to DDoS someone who hits your server off? The other day someone came on my server and said they would hit us off so I grabbed his IP in case he did. Well he hit the server pretty hard and we all crashed. I put his IP in and bam offline for 9 minutes. Who was in the right? None of us, me, or him? I think i did a favor to other servers because he said he did this to the last server he was on.Iguess he was going to small servers and DDoSing them... what a scumbag.