"Here, I brought this," he said. "I realize it disrupts the routine, but don't worry -- you can still throw me out on my ear after you've finished a glass of it."
Harry's learning from Snape -- the best defence against a strong offence is to beat them to the punch! Also known as "using sarcasm and nonchalance to conceal vulnerability". With Ginny he just gets tongue-tied; with Snape, he makes the effort to conceal what he's feeling (maybe even from himself?)... and what you think it worth hiding is a pretty good indicator of your emotional state.
"Because that's…. No, that's absurd." "Why?" "Because it's your idea, and all of your ideas are absurd by default."
I adore your Snape. :D He's not one to let friendship get in the way of the perfect insult!
The ending is adorable and extremely sweet, too -- the first meeting they've had without a time limit, the first time Harry has really been to Severus's home in a permanent context. I love Snape's uncertain pause and slow relenting, and the fact that Harry's straightforwardness sounds more like a riddle than anything he's ever said while intending to misdirect. :D