I almost always hear "RJ45" to identify the 8-conductor ethernet female or male connector - depending on the context. It is universally understood, and there is no confusion about it. There is nothing wrong with using it in everyday conversation.

I have never once heard the phrase "8P8C" used to refer to an ethernet jack. Not once (outside of this thread) - but I have heard it used that way when referring to various 8-pin telco connections - it was a common term of art in the 90s when describing telco installations that used that configuration. When talking about Ethernet, and people are trying to be specific, they usually reference EIA-TIA-568B/A.

There are certain words, like "Bandwidth" - that, might technically mean the width of the band (typically in Hz), but have grown over time to refer to data rate as well. And that's cool - language is versatile that way.

This interesting tangent about common parlance for connector names demonstrates another way in which USB Type-C's adoption trajectory is characteristically similar to 8P8C: people are already giving it a technically incorrect common name, "USB-C".