This has come up a few times on the forum, so search for it. However, having run into this situation many times before (both as someone who plays the piano and as someone who wanted to get someone else to play), there is an aspect to all this that bothers me tremendously:
Anybody who says s/he is pianist is of course inviting requests like "Play something!". That's only natural, because everyone wants to see their skills. But then, nothing is more embarrassing than to have to say "Well, I havent' really prepared anything". Answer "What is there to prepare? You are a pianist, can't you just sit down and play?". "Ahem, no."
This is the situation that many "pianists" find themselves in. They might have the skills to play Hammerklavier and La Campanella, but they can't sit down and play Happy Birthday at a spontaneous occasion. It has nothing to do with friends not knowing anything about making music or piano playing; it only demonstrates that the pianists know nothing about making music or piano playing! Think about it. It turns out that we are not musicians after all, and we can't "make music".
Most of us, to be quite frank, are more like machines. It seems that "pianists" nowadays can play only at very special occasions, namely competitions/exams/personal recitals. They study for a year or two for a recital, then start working on a new one. All the time, they can't play anything, because nothing is ready. A month into the preparation for a new recital, they can't play the Chopin Scherzo anymore, and the new material is far from being mastered.
What is all this good for? People need to ask themselves why they are playing the piano. Is it for their own and their friends' enjoyment and to enrich their personal life, or is it to be able to play a piece once a year for some exam? The answer will depend on one's personal goals, of course.
Of course, in the olden days, pianists were expected to just sit down and play anything and whatever the public requested. These skills are mainly non-existent these days, and it's a pity, because many people have the technical prowess, but unfortunately, they don't have the musicianship. I wish I could do it, and I always marvel at some kid in the store who on the spot improvises something. We need to admit it: without having something memorized or having the sheets in front of us, we are lost!
I hope this touched on some of the aspects that underly your original question. To answer your question more directly: Yes, sit down, learn some of those pieces, and you'll spare that embarrassment for the rest of your life.