Wikipedia:BNBR

BNBR stands for be nice, be respectful.

We were there first with wp:NPA.

BRBN on the other hand is leet for be right back now.

References

https://acronyms.thefreedictionary.com/BNBR
https://www.lingo2word.com/lingodetail.php?WrdID=365099#:~:text=The%20word%20brbn%20is%20used%20in%20Texting%20meaning%20be%20right%20back%20now
[https://help.quora.com/hc/en-us/articles/360000470706-What-is-Quora-s-Be-Nice-Be-Respectful-policy- What is Quora's "Be Nice, Be Respectful" policy? – Quora Help Center]