When a male screams in a Boston accent while having a rod painfully slammed into his ass, usually occurs during the hazing ritual of some Frat's. The buttercup demonation is still unknown, however, when asked why it is called "buttercup" most victims flee away, screaming in terror.
"Hey Bobby, would you care to rush Gamma Alpha Yeti with me? I promise you, we don't perform the BostonButtercup on our rushes!"
a buttercup is when you cup your asshole with your hand and fart while closing your hand into a pocket hence creating a area of pure ass for you to offer to the nearest friend or foe to sniff..