The more comfortable you are with discussing your symptoms, the more comfortable the other person will be! It's been my experience that most people are far more accepting of my skin than I imagine they will be. Find a way to work it into the conversation... for example, maybe when you're discussing family you could bring up that psoriasis runs in your family? It's not usually difficult for me to find an "in". "Hey, would you like a muffin?" "Oh thank you, but gluten aggravates my psoriasis!" Or possibly "You smell like coconuts, is that your lotion?" "Yes! It's the best for my psoriasis. Oh, you've never heard of psoriasis? Allow me to explain...". Be confident and trust in the goodness of others.