No it wasn't a joke, and I wasn't trying to insult you. But I was insulting solipsism. Really, it sucks. It contributes nothing insightful. Um, sorry if you did take offense.
Well, I wasn't questioning the existence of an external world or of other minds. I was questioning our ability to discern the mental models under which others are operating. There may be any number of models that produce similar behavior.
Let me give you several examples.
I occasionally converse online with a rather brilliant person who has Asperger's syndrome. As he has described it, in a social situation he determines how to behave in response to others by quickly and dispassionately running his way through a series of carefully worked out schematics. By doing this he usually manages to appear engaged and appropriate in a manner that more neuro-typical individuals report being able to achieve spontaneously.
I have two friends who are schizophrenic. They have each honored me by describing some of the inner processes they are experiencing while appearing perfectly typical in their outward manner. My one friend has bouts of several minutes out of every hour in which all of reality shifts so that the evidence of each of his senses takes on a sinister cast. With great discipline he chooses not to react except for rare occasions in private. My other friend hears voices that tell him horrifying things. He believes what they say, but generally chooses to behave as if he did not. His friendship with me is based on the assumption that I do not know that I am being controlled by evil forces and therefore I
think that I mean well. For him, if he is to have friends, that has to be enough. I simply do not experience inward states that correspond with what either one describes.
I am an extreme introvert. For me being with the people I love is painful. Every second. Every word of every conversation. It's exhausting and I am mostly angry. I doubt that more extroverted people would even describe what I feel when I interact with others as love. Maybe they would. I don't know. The way extroverted people act leads me to think they feel differently, but then I behave as if I felt differently than I actually do, so I don't know...
Yet, a stranger watching me engage in a conversation with any of the above persons might be tempted to think we are all quite simpatico, giving and gaining something similar from the encounter.
It's all a complicated dance really, our social constraints the formal steps.