I have a friend that i guess you could say holds a pretend Mass. He has a cup that he uses as a chalice and pretends to be a priest and does all the things the priest does at Mass. He does not use real vestments or anything but I was wondering if it is a sin for him to do that. He knows that the crackers he uses are not the true body of Christ, but is this a sin or not?
Assuming that your friend is a child, there is nothing wrong with children pretending to have a Mass. Many a priest or religious has found that their vocation through such childhood explorations of the Catholic faith.