Greatest Ad-libbing

This wasn't actually an ad-lib, the line WAS in the script, but the timing could not have been more perfect:

(Door completely falls apart.)
"Oh...I didn't hear you come in."

I was playing Jan in Grease, and right as "Mooning" was about to start, Roger says "I wish you were there too". I say "You do?" and the music starts. However, on our last performance, the music didn't start. I said "You do?" and then nothing! I looked at Roger, and just said "Well, I'm really glad you wish I was there too."
He said "Yeah. That would have been cool."
Me: "You really wish I had been there?"
Roger: Yeah! We should sing a song about it!"
Thank God, the music started just then! We were so freaked out, and EVERYBODY knew. It was the worst spot to try and ad-lib. We just couldn't make it work! To this day, every time we see each other, we say "We should sing a song about it!"

I have one just from today at my camp during my first period where the Acting, Plyawriting, and Directing class (I'm in Directing) all work together. The Playwriting class had to write "fractured fairytales" and the directors and actors had to put them together.

Well, during this Cinderella one, it was at the crucial point where The Prince was supposed to find Cinderella's glass slipper. So, when the girl playing Cinderella ran offstage, she forgot to drop her shoe, and the guy playing The Prince just looked around for a couple seconds and pantomimed picking up a slipper and quietly shouted "A shoe!" Finally, Cinderella threw her slipper onto the stage and The Prince picked it up and shouted "Another shoe!" And it the most hilarious thing. Because of this, when The Prince went to find who owned the slippers, he cleverly brought two shoes with him. It was briliant.

Also, yesterday I went to see the final performance of a production of High School Musical at my high school. There's this one scene where this geek wants to ask out Sharpay. So he says "I was wondering if maybe sometime you'd consider..." and there's this short pause. You can tell the line's supposed to be "going out with me" but actually what he really does is get on one knee and shouts "marrying me!" and he even has a ring with him. And it was so unexpected and hilarious. My high school is notorious for ad-libbing on the final performance of every show.

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Sideways Stories from Wayside School: During the scene where Mr. Gorf has the kids trapped in the classroom and has stolen all of our voices, one of the little kids playing a dead rat came running across the stage, and without thinking, we all reacted the way we usually did when this happened - by screaming at the top of our lungs. A moment later, when the rat was offstage, I looked around and said innocently, "Hey, we got our voices back!"

That was also the performance where an apple rolled out from behind the teacher's desk across the floor (it was supposed to be hidden back there after the kids did their transformation from apples back to kids at the very beginning), and without thinking, I yelled "ERIC!!!", ran over, grabbed it, and stuffed it in my backpack. That was a fun one for people who really know their Sideways Stories stuff (there's three kids named Eric in the original story, though none of them were in the show.)