I had a couple of good ones as an ADA in municipal court, but my favorite was where before a DWI jury trial the defense had disclosed some enormously long list of potential witnesses, just absurd. We couldn't get a hold of many of them, the attorney was very evasive about who they were or what they would testify to, just some slimy defense work.

Anyway, I'm able to reach a woman on the list a day or two before the trial begins, and she completely destroys the defendant's story--like she is the perfect eye witness, completely neutral, and I would never have heard of her otherwise. We go to trial and I put on my case, check the boxes with my witnesses, and then I rest and the defendant takes the stand and tells his absurd story about how he wasn't the one driving the truck, and the defense doesn't call anyone else; pretty standard stuff for a criminal trial.

Judge asks for rebuttal and I call Ms. So-and-so from the defendant's witness list. Defense attorney gets angry, asking who this is and why am I calling an undisclosed witness and I shrug, "Hey, you disclosed her"--they'd clearly never spoken to her, just putting her on the list to mess with us.

She gets up and testifies that she saw the defendant wreck his truck and stumble out of it. She and her friends went up to the guy and asked if he was ok, he looked around and yelled "I've got to get out here!" and ran away. The jury laughs while she tells this story and then deliberated for (seriously) about seven minutes before finding him guilty.