Anyone who (likely) intentionally writes the word “snicker” wrong to include a slur doesn’t think the actual bad stuff in America is bad.
Snigger is just a variant form more common in the UK, where snicker is the preferred one in the US. Though I wouldn’t put it past a 4chan user, it’s also a perfectly normal word they may have learned being taught and exposed to UK variants of English.
That’s so weird, I’ve literally never seen that form used even by people from the UK.
I guess it’s plausible that they’d just write it like that, I guess.
The secret third option is that they know that it’s a way of spelling it and prefer to use it because hehe n word.