First of all stop putting yourself down. You called yourself a horrible person and a scumbag. Would you ever walk up to a complete stranger and say those things. I seriously doubt it, so why do it to yourself? We have to live with ourselves 24/7 and while we can't control what others say or do to us. We have complete control on how we treat ourselves. You need to respect yourself, be kind to yourself and most of all be a friend yourself.
And as for as feeling guilty for not answering your door to your rude neighbor, so what. You can't change it now its in the past. Im sure if he needed help he found assistance elsewhere. You said he ignored you when you tried to be friendly. So excessively ringing your doorbell could be an indicator that he wanted to complain about something.
I suggest you set one goal for yourself today. So crawl out of bed and force yourself to get a quick shower. I guarantee it will help you feel better. Then everyday write one thing your grateful for. I know you think your so depressed you cant think of one thing. But you can, I know you must be grateful for psychcentral.
One more thing are you on medication to balance your moods?
Best wishes