It’s one of thePriceline commercials with Shatner. What is the meaning behind the thing she does at at 00.19? what does that facial expression convey? I’m assuming it’s not some sort of epileptic episode 
Shrug with rolling eyes, indicating embarrassment at her boyfriend’s smug behavior. Possibly embarrassed agreement.
I read it as “yep, he’s going to get what he wants.”
More as “Yep, he does always get what he wants.” Which triggered Shatner’s “protective Daddy” mode, which leads to the high dive.
I’d call it a facial shrug, agreement with resignation, and a little embarrassment. Her facial expressions are what make Kaley a better than average actress, especially in the hot blonde category.
I agree with all of this. I find her so endearing and entertaining and you just made me realize it is precisely because of her facial expressions. I like that look she get’s after someone says something insulting and it’s kind of a “whoa, okaaaaaay look”.
And to boyfriend, “up until this moment you could have talked your way out of this and left through the door, but now, window it is”.
Whenever I see those commercials I like to pretend that that’s actually Penny from Big Bang Theory in a big acting gig. That’d be a fun episode of Big Bang Theory when Penny discovers she’s going to be working with one of the guys screen idols. I wonder if her acting career takes off on the show if they’ll have her get a commercial gig similiar to the priceline job.
Did you see the disclaimer: “Dating the Negotiator’s daughter is dangerous. Do not attempt.”
And I read her expression as a mild blush, signalling agreement that the boyfriend is going to get what he wants, i.e. her.
I never noticed her except as a pretty face in the crowd, and at first I didn’t know it was her in the Priceline ads, reacting, “That pretty blonde has comedy chops! Who is she? She needs a series.” (sheepish :))
Which is funny, because it’s very much an overexaggerated facial expression, a kind of mugging. Just like Shatner.
She previously worked with both John Ritter and Katey Sagal in 8 Simple Rules, so, yeah, she’s got comedy chops.
KC’s facial acting pretty much carries The Big Bang Theory. A line’s not funny til Penny’s reacted.
Well, maybe someday… 
I read it as saying, “look he’s a smart guy, he uses Priceline, give him a chance”, whilst knowing deep down it’s a hopless gesture.