Think Im gonna make one of those. The reactions will be priceless! 
I think a certain age group would not even know the difference
Like me. I know there was a music band called Nirvana, but to me the T shirt meant the three achieved nirvana, or so they think. Nirvana comes from Buddhism, meaning a transcendent state in which there is neither suffering, desire, nor sense of self, and the subject is released from the effects of karma and the cycle of death and rebirth. Their faces shows contentment, or mindlessness to me, hence my interpretation.