expression
apologies for tweeting to someone you don't mutually follow
Twitter jargon; abbreviation of ＦＦ外から失礼します. Used when replying or tweeting at someone who doesn't follow you back, acknowledging the breach of netiquette.
ＦＦ外失します。突然のリプライ失礼します。
FF外失します. Sorry for the sudden reply out of the blue.
ＦＦ外失ですが、その話題について一言。
FF外失ですが, just a word on that topic.
The full, more formal version of the same phrase; used in the same context but less abbreviated.
Abbreviation of the Twitter phrase ＦＦ外から失礼します (FF外から失礼します), where ＦＦ stands for 'follow-follow' (mutual following) and 外 means 'outside'. The exact origin is uncertain but it emerged as internet slang on Japanese Twitter.