FSIF
Fucks Sake I Forgot: an abbreviation for when a person forgets what they sent on Snapchat and the text won't fit on the picture so FSIF is used, similarly to omg and fml.
Snapchat 1: "Omg I can't believe you did that?"
Snapchat 2: "Sorry believe I did what?(FSIF)"
Snapchat 2: "Sorry believe I did what?(FSIF)"