I'd heard of "jumping the shark" (where something goes beyond the realm of believability and thus begins a slide into the sunset, named after the famed "Happy Days" episode where Fonzie literally jumped a shark on water skis), but I'd never heard of "tipping the tuna" until I read this Ross Mayfield post about the social networking site Twitter. It sounds like tuna-tipping is the lead-up to shark jumping, from what he says.
I know meeting planners are constantly tasked with outdoing what they did last time, so in effect no good deed goes unpunished—the better you do your job, the more is asked of you next time around. But while thinking of how to top yourself, take care to stay true to your mission: The goals and objectives of the meeting itself. Otherwise, you may end up leaping over sushi and losing credibility, or at least relevance. Even if you're just tuna-tipping, attendees will smell something fishy going on.