...to be honest I wasn't even aware that it was British (I'm L3 but I use RP as reference). I picked it because it sounded a bit less blunt than "fuck off", but not much.
In other words although I'm not a native English speaker (L3 = third language) I tend to use the language as some British people do. As such I might end using terms that are mostly restricted to the UK without noticing that they may not be understood by others.
That's the case with "sod". It's something like "damn" or "fuck". Sometimes also used as a noun to convey contempt towards someone, as in "that sod" = "that fucker", "that poor thing". And "sod off" = "fuck off", but it feels a bit milder.
[RP = received pronunciation. I used it slightly off-context here but it's just a reference anyway.]
The origin of "sod" as a slang term comes from British English, where it has been used since the 19th century. It is derived from "sodomy," which refers to non-procreative sexual acts, and has historically been used in legal contexts with negative connotations. Over time, "sod" became a more generalized term of abuse or insult, detached from its original specific meaning related to sexual acts.
In the context of "sod off," the term "sod" is used as a derogatory noun, but it has become somewhat less offensive over time, often considered more cheeky or informal rather than a serious insult. The usage of "sod" has expanded beyond "sod off" to include expressions like "poor sod" (a term of sympathy for someone in an unfortunate situation) and "lucky sod" (someone who is particularly fortunate), showcasing its versatility in British slang.