Mine is break in and warm up, once a piece of stereo equipment is sufficiently broken in.
There are certain audio taboos we’re loathed to violate. High atop my list would be plants atop speakers. (But it behooves us to be diplomats if we’d like not to sleep on the couch)
Diplomacy aside, we purists rarely tolerate violations of our taboos and sacred rituals.
Some taboos make sonic sense: plugging all your equipment into an AC extension strip, stacking a turntable atop a power amplifier.
Perhaps more prevalent than taboos would be the sacred rituals which cover everything from record handling, room light levels, seating positions, warm-up time, and source protocols.
I never start a listening session with vinyl. My ritual is to get the system warmed up and me adjusted to it with known digital references. Then, and only then, am I comfortable switching sources.
What are your audio taboos and sacred rituals?