[Sharlin]

Yes, many languages use `_` as a placeholder name, and at least in Rust any name starting with `_` is considered intentionally unused.

[hunter2_]

Aside: many IRC clients would auto-append _ when registering a nick if the desired nick was already registered. Why _? Who knows.

[Sharlin]

Probably because it has no specific meaning and being almost whitespace is the easiest to mentally ignore out of the set of valid nickname characters. `-` is another candidate but a programmer used to C-like languages will likely intuitively pick `_` just because it’s valid in identifiers unlike `-`.