Questions about the undershirt

I can't imagine any scenario where Donald would have put his shirt on and left his undershirt off. Worst case scenario --he had his clothes off with the priest--why would he put his shirt back on but not the undershirt? Best case scenario --the priest buys him a new shirt that fits better. Why would put the new shirt on but not the undershirt? Unless the new shirt fit well but the undershirt was too small? I'm just trying to make sense of the undershirt since it seems like such an import detail.