I'm surprised it wasn't just "and all vowels" with the same reasoning, or at least 'a' (because I can more readily think of examples than for, say, 'e').

I suppose, though, there's an attraction in using b32 rather than b29... (Though I notice mid-word apostrophes are double-tap-selectable at least on macOS, so perhaps swapping 'a' for ''' would be advantageous, if more complicated to explain.)

The two "worst" swearwords that pop into mind both have "u" in them. Meanwhile, the swears with "a" in them seem to be the tamest of the lot.

"Tameness" varies extraordinarily by region - an infamous example being 'twat' which throughout the UK ranges from friendly to vulgar.

Regardless of variance, I don't think I'd regard either the above or the name of a fat character in Austin Powers as "tamest of the lot".

I find it interesting that you're willing to say "twat" but not "bastard". I admit that I didn't think of either of those words, though I think they're still much tamer than the ones with "u" in them. Really what I was thinking of was "crap" and "damn".

I once had a moment of panic after coming up with and shipping a custom scheme along these lines, when I realized there was a decent probability of generating accidental profanity. Afterwards I came up with a filter, and we spent a fun day filling it with every nasty word we could think of.

That's actually pretty brilliant