...You can't open your curtains because someone might, from the outside, see you open them; and, if you somehow get them open, you must be cautious about looking outside because someone might be around to see you.
...You can't go out in public because you have probably inadvertently developed strange, embarrassing mannerisms/habits through the countless hours alone in your house, so you spend many more hours alone in your house developing yet more strange, embarassing mannerisms.
...You discover that the store you went to doesn't have what you'd come in for, but you just buy something anyway so that the cashiers don't wonder why you suddenly left.
...You spend 15 minutes devising a username because you are afraid that someone might be able to guess your identity based on what you use... And then are still not confident that you have avoided that possibility.
Then, as a bonus:
You Know You're AvPD and BPD When...
...You feel so sick of the appalling dullness of your life that you impulsively decide to walk all the way across town just to escape. Then, finding that you've walked so far that your feet are bleeding, you are confronted by the reality of the situation: somehow you will have to get home. But, you can't call anyone to pick you up because 1. You have next to no friends and 2. The friend you do have will be annoyed/irritated/judgmental if you ask 3. You can't explain your reason for getting stranded, so the friend will be even more annoyed/irritated/judgmental. You think suddenly that it is a good idea to hitchhike, and that people are so fascinating you want to meet all of them, but when someone pulls over, you realise that you will have to actually interact with this person who is not only a stranger but also infinitely more unappealing than you had imagined, and so you pretend at that moment that you "got a call from a friend who will give [you] a ride." Your only remaining option is the bus, and it takes 5 minutes of preparation to make your way to the bus stop... And then, for good measure, when you are sitting at the bus stop, two homeless guys starting having a yelling match, with you sitting directly in between...