So, for the record:
Two-year-old boys who want to spend the night with their grandparents quickly lose that privilege when they insist on taking off their diapers and pajama pants in bed.
Now, if the said two-year-old is interested in learning to use a potty, then there can be some negotiating - although his mother will probably still insist that he keep something on that little bottom.
But as long as there is no control? Well, keep the diaper on.
We won't mention any names, since the two-year-old at my house was already embarrased (to a healthy degree) when his night ended sooner than he had planned.
But he was warned. I assure you. (And, he knows how to keep it on. I assure you.)