Personally,I don't like shirts with slogans or writing on them,but if you do go for it.
An I sure don't feel I have to explain to anyone as to why im wearing a kilt on the back or front of a tee shirt.
If they want to know let them ask.
Its like the (Real Men Wear Kilts) logo.Hate that. I think theres a Kilt maker that uses that slogan an I personally wish they would drop it.
If you feel your making yourself feel more comfortable wearing a kilt in public by having some silly slogan on your shirt,than don't wear a Kilt at all.

Sorry if i'm sounding like a grouch today,but some things just tic me off.

"The death of fear is in doing what you fear to do."