A sensation of supreme dryness and lack of moisture in the mouth, akin to drinking 8 pints of sand after playing basketball, that wakes the victim up in the middle of the night and creates a feverish, panicked, and borderline predatory need for cold, refreshing liquid. Also known as after hours cotton mouth on steriods.
Jill: So, I have a vague memory of you exploding out of bed, knocking over the TV, and making dinosaur sounds last night. Bad dream?
Frank: No, I woke up with Midnight Mouth and had to chug half a gallon of orange juice.
When an individual realizes that the story they're telling makes them look incredibly stupid, and attempts to counteract this effect by quickly explaining that the activity being described occured during childhood, or at least a decade prior.
Dave: So, I had this funny habit of collecting the prettiest fall leaves I could find, but in the end, it...I mean...well, I was 11 at the time, so you understand.
Bill: You just gave a YouthScuse. I saw you collecting autumn leaves three weeks ago.