This is irrelevant. You don't have to show brick every time. We say sugar is sweet. No body experience how sweet is defined by other. Still we all believe it is sweet.
That's a bit different. The definition of sweet is basically defined as "the experience you get when eating sugar". It doesn't matter for this purpose if that experience is completely different for you - all that matters is that we both know that "sweet" is basically a synonym for "your experience of sugar".
Note that this definition allows you to predict a lot of things:
1. You can predict that you'll have the same experience when eating other things which are not sugar, but which you know cause the same experience in you.
2. You can predict, at least in broad outlines, whether people will find this experience pleasurable or not (again, on average, broad outline, but still better than chance).
3. You can predict that someone without a sense of taste won't experience anything when eating sugar.
That's why this definition is meaningful. Of course I can play word games all day about "can you show me 'sweet'???". But those are word games that are trying to hide the idea of what a definition is and what we use it for.
