The Invasion: A dinner companion casually eats from your plate uninvited.

The Defense: Head her off at the pass. Before you dig in, “an elegant approach is to place a small sample of your dish on your bread plate and pass it to your dinner companion,” says Markus Draxler, the maître d’hôtel at the acclaimed French restaurant Daniel, in New York City. He also suggests asking your waiter to have a portion split for you in the kitchen before the meal is served.

If the portions are small, however, or you don’t feel like sharing even one bite, a comment like “I’m so starved — I can’t wait to eat every single thing on my plate!” can discourage a scavenger from focusing her crosshairs on your pork tenderloin. And when the waiter takes your dessert order and asks how many forks you’d like, saying “One, please” will give your dining companions the signal to keep their tines in their own tiramisus.

The Invasion: You are on a group vacation but crave some alone time.

The Defense: Whether you’re traveling with friends or in a tour group, sometimes you need a vacation from your traveling companions. “I’ve had this happen on numerous occasions and find that it’s best to be honest,” says Stacy Small, a Florida-based luxury-travel consultant and the president of Elite Travel by Stacy. Prearrange a few activities just for you, like a spa treatment or a golf lesson, and simply explain to the others that you set up some appointments ahead of time. Or, suggests Molly Erdman, a comedian with the Second City troupe, in Chicago, pick an activity obscure enough to turn off the rest of the group (“Hey, I’m going to the sawdust museum tomorrow! Who’s with me?”) and then savor your freedom once the group has set off in search of more traditional sights.

Another strategy is to be the earliest riser and get a start on the day before your friends are even out of bed. Or, says Kim Izzo, coauthor of The Fabulous Girl’s Guide to Grace Under Pressure, let the group members make their plans for the day, then politely bow out before they depart with “I’m going to hang alone by the pool today.” “Your friends may be glad you’ve introduced the concept of spending some alone time and take advantage of it themselves,” Izzo says.