Why do I have to say it twice?

I was helping Trevor clean up after a trip to the potty yesterday, and he casually told me not to use too much toilet paper. After I went to grab the second piece of toilet paper, he again mentioned casually that I should not use too much toilet paper.

After I flushed and helped him pull up his pants, he told me, with much exasperation, "I don't know why I have to say it twice."

Parents. Can't live with 'em...