It would have been the Whiskey Bon Bon incident from Nisekoi all over again... wait, is that really a bad thing when only the main pairing are partaking, instead of an entire room of girls who can't hold their liquor suddenly going kissy-crazy for the guy they're all infatuated with, even if most of them aren't willing to admit it openly? And the one that is open about it is rather unpleasantly manipulative most of the time...
I'm sure I've seen the whole 'alcoholic chocolates or beverages reveal character(s) can't hold their liquor and start acting wacky' in other anime or manga, but that's the one that sticks out for me right now.
Nisekoi did it a second time with amazake, even, in the manga.