Gotta be the most archaic language still in common use.

I mean not saying it doesn't have legitimate uses, fast well tested and a few procs with the right options can accomplish a the equivalent of a lot of Python, and I only ever learned enough to run a few datasets and port some old code to python/r/vba, but observing the crazy ass shit people did to implement any kind of logic or data transformation was enlightening. Many many "wait people actually do this" moments. Like an entire ancient programming paradigm I never knew existed.