[T Minus Four]

if I were trying to prove this was so to a Catholic, what would I reference?

Or maybe I’d better not - if they are violating this out of ignorance, and then I tell them, and then they scoff and don’t obey, well......

[annalex]

It varies by country -- or, rather, by the Episcopal conference. In the US, the obligation is to do an act of penance, but the faithful are free to choose the nature of the act. The decree is a bit vague, but leaves no doubt that the obligation is still there throughout the year:

Pastoral Statement on Penance and Abstinence

It is all unpacked very effectively in this article:

Are Catholics Supposed to Abstain from Meat Every Friday?.

The article, by the way, convinced me in the wisdom of going away from the blanket insistence on abstinence from meat. In a country like ours, it is no great sacrifice to give up meat, readily available the other 6 days of the week.