I'd take that as a sign you need to fight against your SA, mate. I understand it's a horrible situation to be in when you're that anxious, but if you're unable to answer the door to someone, time to get to grips with it, really. Order self-help books, anything, but you need to sort this out.
Talk on here if you want to, there are people on here happy to offer advice.
First of all, what do you feel about answering the door to collect your takeaway that worries you so much? The delivery person making fun of you? The delivery person being female? The fact that it's an unhealthy meal and that people will know you eat it? The fact that someone will see plainly that you're about to eat? What worries you about it?
The more information you give, the more likely we can offer a solution.