As far as Tony's concerned, social acceptability went out the window at about the same time as his sight vanished. He figures out what Steve's doing as he guides his hand to the bottle, debates with himself for a second, and makes a decision.

"Steve, seriously, it's okay. If I can't trust Captain America not to give me something that's going to slice my hands off, I can't trust anyone. I appreciate the gesture, but it's fine. You have something to give me, just hand it to me."