Bucky saw where Dean had placed the vial but ignored it still. Even if he didn't want to worry about how his own body would react, he hardly thought a headache would be the thing to use something like that on. Resources could be scarce and it wasn't infrequently that people were hurt.
"It's fine." Bucky said, tipping back a sip of his drink to prove the point maybe. "I don't get drunk, but it's a habit maybe."