[athenot]

Normal body temperature was defined† in Celsius, at 37ºC; this explains the decimal when used in Fahrenheit (98.6F). So even that argument of convenience doesn't hold.

† Yes everyone's baseline temperature is slightly different, but that just makes the decimal on the Fahrenheit scale look even sillier. And fever definitions are also keyed off of Celsius: 37º to 38º is "low grade". Sure, it's an arbitrary convention but it's the one adopted around the world, including in the US (98.6 to 100.4).

[shawabawa3]

Whether it's off by a degree or 2 doesn't matter (as you said body temperature varies)

But why is 100 ~= body temperature more useful than 100 = boiling water?

Why is 50 being kind of cold more useful than 10?

I don't get this "Fahrenheit numbers are more useful/convenient/understandable" argument

[tantalor]

As a human person, temperature relative to my body is more useful than the boiling point of water at ~100 kpa.

Anyways, in Titan's atmosphere water boils at ~110 C, so much for "100 = boiling water".