When one of the grown-ups starts on a temper tantrum about the flavor of his parfait cup, I stand there, silently nodding, maintaining eye contact. All the while, though, I just picture large worms crawling all over their face while they're still alive. And if one of the worms slips off, I pick it up, reach over and drape it back over their lips.
This last part is done in pantomime but my naturally sweating hands' dampness lends the right level of discomfort to the affair.
Few do, but if they ever question my behavior, I just tell them I plan on buying a large pickup truck and that quiets them down.