Wise Thoughts Unsaid and Unremembered

The perfect reply that I hadn’t yet thought of
but figured out later? I have had a lot of;
but the problem is that now they still can’t be gotten,
for though once I had them, I now have forgotten!

It’s true.  Great retorts are jewels in the crown,
but truer that one has to write them all down!
And it’s best that you write them down lickety-splickly,
for though they come slowly, they seem to go quickly!

The Prompt:  We’ve all had exchanges where we came up with the perfect reply—ten minutes too late. Tell us what it was, being sure to sign off with your grand slam unused zinger!