In the case of the shirt, there isn't confusion about if it is a soft drink, but a lawyer could successfully argue that a customer might buy the shirt thinking

In the case of the shirt, there isn't confusion about if it is a soft drink, but a lawyer could successfully argue that a customer might buy the shirt thinking it was a coca-cola shirt. If the coca-cola trade dress did not exist, it is extremely unlikely that a shirt with that design would be marketed.