- When you're able to clearly identify someone who is mental through the natural look on their face, despite them acting in an otherwise rational and sane manner.
- Ideal as an insult; typically a step up from mental or mental in the head, but can also be used as a description of how someone looks. For example; if they genuinely look as though they are about to massacre an orphanage.
- Honest? Are you mental in the face? Imagine how that would look.
Thomas Leone is mental in the face. But if you ever say this to his mental face, he will roundhouse you in the prick.