My oldest did this a couple of years ago. He'd been using adult spoons for a while, but one day I gave him a jello with a baby spoon -because I prefer to eat jello with little spoons (it makes it last longer!) He was outraged and stomped back into the kitchen to fix the injustice. He was about to grab a large plastic kitchen spoon when I asked him what he was doing and he responded that he was "a big boy". I showed him how I was also eating jello with a little spoon. I can't recall if he accepted my assurances, or if he grabbed an adult spoon, but at least he gave up on the kitchen spoon idea! Of course, with a comic, you want to push the joke.
For the bonus panel, I brainstormed on other big eating/drinking ideas. I'm not actually a big drinker, especially with wine (yuck!) but sometimes you have to lean into the stereotypes. I've seen those giant novelty wine glasses you can get, so I thought Fran with one of them would be funny. Here was the reference picture I used:
