Of course, there are plenty of graphic t shirts that are basically variations on a theme: how many examples is there that use the same Batman symbol, just changing the placement and size and the background color of the shirt it’s on? That way, even where one’s tastes overlap with others one can enjoy a measure of uniqueness, because there will be more people who like the same thing but have different shirts for it than that have the exact same one. Even in common interests, people can be distinct.
The only thing that’s needed is to look through what’s available and pick out a few one really likes. The differences of people’s tastes are the best reflection of how distinct they are as individuals, so actively enjoying what one likes is the best way to prove how unique one is. The different graphic patterns on t-shirts are a great way to express this, because they deal with a wide range of things that one might like.