[Sometimes she's not sure how much of Spock's clueless routine is him being a pedantic asshole and how much of it is genuine misunderstanding. Deciding to give him the benefit of the doubt, she picks up her glass of synthehol and takes a bracing sip before attempting to explain.] It's an idiom denoting an expression of guilt. You looked as guilty as a child caught doing something they had been forbidden from doing, such as taking a cookie before the proper meal, hence the expression.

[The replicators do their best when it comes to fulfilling dietary requests, but they don't always quite hit the mark. Her plate of good Southern comfort food is a very close facsimile to what she might eat after a bad day back on Earth, but subtle things about the texture or the flavor are just a little bit off. Still, it's worth it to shovel a forkful of mashed potatoes in her mouth and let the buttery flavor spread across her tongue, so she doesn't complain, just watches as Spock examines his chocolate.]

That's dark chocolate, [she points out, watching him smell it. It looks ridiculous, but then again, if he's never eaten it before, it's not the strangest reaction to have.] It'll be a little bitter. Milk chocolate is sweeter and creamier, but it doesn't have as strong a chocolate flavor.

[She rolls her eyes at him, cutting off the skin of her friend chicken and lamenting the fact that it just isn't quite right. Still, she's going to eat it because she's had a shit day, goddammit, and this will make her feel better.] I'm saying it'll make me fat, Spock. Sweets like chocolate go straight to my hips because that's where most human women store fat deposits. "A moment on the lips, forever on the hips," that's what my mother always used to say.