I finally figured out how to do it. Keep nibbling already nibbled piggies and your mood drops and then you can drink more. It takes AGES and leaves you exhausted and it wasn't even worth it. I am not sure what Rocky even gave me for my 'achievement'. I didn't notice anything worth it pop up. On that note, it would be nice to have it 'appear' in front of you to select for your bag, rather than just directly going in there. A bit of an anti-climax to a lot of hard work! :)