And why can't I think of a single witty thing to say to that?

We all seemed to be able to think of wittier things to say.

I am not one of those who have witty things at every body's service.

He said a lot of witty, amusing things, which are still remembered today.

However, whatever may have happened is usually less important than all the witty things that can be said about what happened.

I don't have the luxury of thinking of witty things to say 20 minutes later.

I couldn't think of a single witty thing to say.

He laughed as though that was a particularly witty thing to say.

There are many stories about the witty things that he said.