Abriviation for snap back
Usually found on Snapchat when a user wants you to snap them back

From STEM, an abbreviation short for "Science, Technology, Engineering and Mathematics", a STEMlord is a pejorative term for a particular kind of person who has studied in these areas at university or works in these fields who holds a pretentious, condescending attitude to anyone who has studied in any other fields, particularly the Arts and Humanities. They typically believe themselves to be more "intelligent" and "rational", while generally remaining incredibly ignorant outside of their areas of expertise and having the charisma of a rotting pig's backside.

It means Snap back, referring to when someone says snap for tbh (to be honest) and they want one back.

in terms of snapchat, sb means ‘snap back’

SB/ Sugar baby. A person who would accept gifts, money, or other forms of payment in exchange for sex usually.

noun. (pl. same) also,S13
Comes from a Chinese words

Pronounces Sha bi,means "Stupid Bitch".
In fact, Sha = 傻(stupid),Bi = 屄(pussy).
If you play online games in China or chat with some Chinese lowlives you'll see it many times.

SB Means Sidebar. So if they post something they can use "SB" to say something else