I can't belive I just did that.
I was working on a quilt, and I lined up a bunch of pieces, and got them all ready to chain piece. I went to iron them, and I sewed them together backwards. Instead of pinning right side to right side, I pined right side to wrong side, now off to find the seam ripper.
Thankful it was only 16, and of those there are four from a fabric that looks the same on both sides.