You know how it is. You're at the Evening Filling-up of Beakers, or whatever, and it comes to "exchanging the Peace" time. But how do you know what exchange of peace is appropriate with any given person? You look so much of a fool shaking someone's hand when they're into hugging. And you look more of a fool if you think you're on "hugging" terms but discover that the huggee of your choice just thinks you're at "curt nod of peace" terms.
So the answer is both efficient, and potentially lucrative. T-shirts of Peace, indicating just how far you'd rather other people kept from you. In any case of different levels of peace-sharing, the person expressing a preference for greatest personal space wins. Whereas, in normal peace-sharing situations, they always lose.