If they're drunk how will they even understand what they're signing
Good point. Add a line at the end that says- "I, the undersigned relinquish all claims to my girlfriend/ wife and fully allow this researcher to ravish her without repercussions this evening".
Seriously though, I'm taking a research methods course (kill me now), and we actually learned something about this. Add this line-
"I understand that participation is voluntary and that all answers will be published in aggregate form only." I think aggregate means identities will be kept anonymous.