You know you sew a lot (of mistakes)...

(No, this isn't mine)

 ...when your favorite seam ripper dulls, and you try to sharpen it

on the kitchen knife sharpening rod. :)

And it's a flop. Seam rippers have a very small curve, you know,

and don't fit over a large rod.

Internet to the rescue:

Source 1:

"To sharpen your seam ripper, wrap 000 or 0000 steel wool around a crochet hook or pencil. Holding the seam ripper in your non-dominant hand (left or right) and the pencil or crochet hook in your dominant hand, move the pencil or crochet hook with steel wool wrapped around it in an upward motion. Do this to each side of the "blade" of the rippers. Emory paper will also work."

Sourse 2:

"I have a Bead Reamer. It's a very small, round file. It's designed to be used to smooth out or enlarge the hole inside of a metal or natural stone bead. I'm sure it has other uses, but that's what I've used mine for.

Tonight I got my dull seam ripper out and held the bead reamer at an angle similar to the way the seam ripper is filed. I did three light passes on each side of the ripper and Voila! It worked! My seam ripper works great now. Not sure how long the edge will last, but I thought that was pretty slick.

I paid $2 for the bead reamer at my local bead shop, which seems like a good investment if it will keep me from throwing away my more expensive seam rippers!"