The ASCII art (well technically ANSI art) histogram is neat. Cool hack to get something done quickly. I'd have spent 5x the time trying various chart libraries and giving up.

On a similar note, I like the crude hand-drawn illustrations a lot. Fits the "napkin" theme.

Here [1] is a nice implementation written in Awk. A bit rough around the edges, but could be easily extended.

[1] https://github.com/stefanhengl/histogram