If you take you son with GERD with you to babysit your friend's two daughters and it's his first night with a new form of one of his reflux medications, neglecting to bring a second pair of PJs is a bad idea.
But if you do forget to bring a second pair of PJs make sure you get pictures of him wearing the pink rocking horse PJs that you had to borrow from your friend. It'll be even funnier later than it is now.
P.S. Here's a more manly image to even things out.