When an offender breaks wind in a group consisting of two or more people, during a serious conversation and carries on without recognizing that any infraction has occurred. A Grand Plo Koon is when none of the members of the group shows any reaction whatsoever.
During the annual board meeting, the CEO Plo Kooned relentlessly. The only thing keeping the situation from turning into a Grand Plo Koon, was the CFO's inability to keep a smirk from his face.