It either stands for “snap for snap”, “shoutout for shoutout”, or “spam for spam”
SFS on Snapchat means “Shoutout for Shoutout“. Basically, it means a Snapchat user is looking for a little shoutout on your Snap. The same acronym is used on Instagram too, and it’s used to promote posts on other pages.
If someone asks for a Sfs they will send a picture and you can post it on your story.
One user will tag another in their post to direct their followers to the other’s page, with the aim of boosting their respective follower counts.
Put simply, influencers do this as a way of mutual promotion.
The other user then hopefully returns the favour by doing the same.
In text and chat, it can be used in a number of ways to express a mood or state of being, such as so fucking stupid, so freaking stressed, or seriously funny shit, and is sometimes used to mean sexually frustrated … uh oh.