[marsRoverDev]

Why is this term so familiar to people on HN but like OP I cannot find a single reference to it on Google...

[sanderjd]

I think people are very familiar with "foot gun" which is quite common, and are inferring that since a cannon is a really big gun, a foot cannon is a really big foot gun.

[gr__or]

I think "foot gun" (https://en.wiktionary.org/wiki/footgun) is more common.