Comment 44 for bug 479296

> Once you've logged in as your user, you can probably
> verify with "pgrep pulseaudio" that it is not running as your user.

Sure, but what I wanted was to prevent pulseaudio from starting at all in the machine. Not even once.
I first created file /var/lib/pulseaudio/pulse_a11y_nostart: Better than the $HOME/.pulse_a11y_nostart because it prevents logging whatever $HOME resolves to. But that wasn't enough. It seems that pulseaudio was still called, presumably from the login screen (when it rolled the Ubuntu drum).
I ended up using the brute force approach and renaming the the pulseaudio binary to pulseaudio.off. That worked.

I'll be back here within at most 72 hours, to report either yet another freeze or random segfault (and pulseaudio presumably innocent) or no problem (and pulseaudio still under suspicion).