1. noun: a mother (specify whose mom), who gets fucked in the face (specify by who), or a verb action of doing this.
2. noun: A person, who fucks a mother (specify whose mother) in the face, or a verb actione of doing this)
3. noun: A very evil way to call something/someone that the caller greatly dislikes.
If one doesn't specify it can get confusing.
Also see fatherfuckface !!!
Your mom got motherfuckfaced last night by me!
Why'd you motherfuckface your mom last night?
You dirty, MFF what do you think you're f-ing doing?