Wasn't expecting you to knock, figured the text was my warning.

[Crowley wouldn't like Martin to just show up in the flat unannounced unless there was something actually wrong, but with a little warning, it's fine. It gives him time to say no, on the off chance he might not have wanted company.]

And nah, I thought I'd drink two glasses at once. Unless you want something a bit stronger?

[Desperate times, etc.]