An old reference to a relatively small gathering of people, mostly friends, where about two-thirds of everyone's drinks are spiked with LSD, and the lucky individuals of the party trip out while the people who have no LSD in their drinks are responible for babysitting the trippers.
Buttons has also become a slang term for mescaline, peyote, or psilocybin mushroom caps.
PERSON 1 - "John's party last night turned into another game of buttons."
PERSON 2 - "Shit dude, were you trippin' face?"
PERSON 1 - "Na bro, I had to babysit Greg who kept telling me that he was trapped in a glass of water..."