Is 'rapier' not a word used in US English? It's a type of sword. It's nothing to do with 'rape' if that's what you're thinking. It's neither spelt nor pronounced anything like 'rape'. I can't see any possible confusion or connection at all but several people are making it in this thread.
On the other hand, as a native English speaker, I understand the word to be pronounced such that it isn't much of a stretch to put it between "rapey" and "rapiest". While neither of those is, I think, particularly well established as a word in "proper" English, they are understood and used in less formal contexts (if jocularly).
I don't know where all of this leaves us.
I know the word and its meaning and my initial reaction was negative because I thought "this has very little metaphorical value for a physics engine." You think of kinesis, movement, reactions. "Box" makes sense because it's a physical constraint with coming and interesting physics effects across its physics. Rapier is - to me - just an inanimate object.
But imagine you don't know the word. It could be jarring. And unlike words evoked by a sibling reply (paper, rap, etc) it's not nearly as commonly known or used.
Either way, this is a super cool project. You have to love it when someone puts their mind to it and produces something of this quality as open-source. I'm especially interested to see if this might kickstart some of the Rust efforts around GPGPU, which is currently so-so, since a cross-platform solution there seems like it would definitely be a benefit for this kind of project.
I hope I'm not misrepresenting your argument, but the way I understood it sounds very US-centered.
This sort of thing happens sometimes (see: Ford Pinto)
I looked at is as implying lightweight, nimble, and functional efficiency for small-scale uses, much like its namesake. I would assign much different metaphorical implications to something named "Zweihander" (Germanic two-handed sword) or an even more esoteric French polearm name such as "Bec de corbin" (a name probably only known to hoplophiles).