The Doctor was feeling slightly better after his lunch with Jenny - he's been quite jubilant while with her, but when it had come to the time to go their separate ways for a little while, the pain had started to kick in once more. He didn't really want to be alone, but at the same time... he didn't want to have to explain himself to anyone.
When the door went, he stupidly didn't think it would be Rose, so when he opened to see her standing there he wasn't really prepared. And so, childishly he swung the door shut again without so much as a 'hello'.