This is actually the main reason I walked away from vegetarianism. It's too socially alienating. In many parts of the world (including many places in the U.S.) food is love. Turning your nose up at food cooked and offered to you with love from friends and family only serves to damage relationships and disconnect your further from society. Eating a meal cooked and served with love surrounded by family and friends nourishes the soul.
Obviously if you have an allergy or serious intolerance you're going to want to stay away from those foods, but for most people it is not a big deal to eat outside the paleo sphere once in a while.
I'm not saying you need to binge on every processed carb at the table, but if the soup has potatoes in it the world is not going to end. As much as possible, try to load your plate with meat and veggies and avoid or minimize the breads and grain-based sides. I've also found I can usually get out of dessert if I claim to already be too full from the fabulous dinner. But, no matter what, don't waste time or mental energy feeling guilty. Enjoy the time you spend in the company of family and friends and go back to your way of eating when you get home.
Now, the above refers to eating at the homes of friends or family. If you are at a restaurant, you usually have the ability choose your own food. Just make sure you ask questions before you order. You can't expect the restaurant to take food back because it contains grains or dairy if you didn't ask about it before you ordered it. But again, don't stress out about. There is almost no chance the food is going to be cooked in the same way you would do it at home. Even the best restaurants tend to use industrial seed oils (or worse) in their cooking.
What you eat on a regular basis is far more important than what you eat when visiting friends and family every once in a while.