The phrase "best thing since sliced bread" should be "the best thing since splinter-free toilet paper"

Fun Fact: Pre-sliced bread was invented only 2 years before splinter-free toilet paper, which leads me to suspect the reason sliced bread is "the best invention ever" is because some people were wiping their ass with the sliced bread instead of risking a splinter in the sphincter.

It may also explain the term "shit sandwich."