So, you've exhausted your supply of clever remarks, have you?
Don't worry, friend. We've got you covered. Here are some emergency phrases to get you out of this sticky situation:
"Well, isn't that just peachy!"
"Oh, joy! I'm so glad I wasted an hour crafting that response."
"I'm shocked, SHOCKED, that I'm running out of things to say."
Or, if all else fails, just pretend to be interested.
*yawn*
Good luck, and remember: sarcasm is just a coping mechanism for the soulless void within.