Microsoft is open to a collaborative search deal with Yahoo, “very open” apparently, but CEO Steve Ballmer again nixed the thought of revisiting an acquisition, according to both the AP and Reuters. The AP quotes him as saying, “Let me be clear. We are done with all acquisition discussions with Yahoo.”

It was the first time Microsoft twitched since Yahoo publicly acknowledged that it’s looking for a replacement for CEO Jerry Yang, the guy who beat off Microsoft’s $47.5 billion bid with a stick.

In the same breath Ballmer told Microsoft’s annual stockholders meeting Wednesday that Microsoft isn’t immune to “current economic realities,” which may be Ballmer’s real reason for resisting.

And it’s just going to get worse for Yahoo whose shares are now a third of what Microsoft offered. Maybe Yahoo ought to try dropping its poison pill defenses.

There are no discussions going on between Yahoo and Microsoft right now Ballmer said.