The act of telling people off that consistently misspell words in their statuses and in other aspects of life. The "your" can be substituted with "them" when the action is towards someone else or to "my" when regarding yourself (or your shelf). The "shelf" is supposed to "self" in proper English. Can also be used as FMS, FYS or FTS as abbreviations.
For the fact that you always misspell on Facebook, you can go fuck your shelf!