A frat injury. An injury, to a beastly frat
guy, that he suffers during a night of drinking. At the
time of the Frinjury, you're like "ow that hurts." You then keep crushing, and think nothing of it.
The next morning, however, when you wake up, god help you. Not only are you in a lot of pain, but you remember the "spill" you took, or
whatever caused the Frinjury. You're reaction is then "wow, that's why it feels like I shattered my knee
cap," or "that bruise is the size of a country." (usually with the bruises, someone else notices, thus leading to a fratty interaction.)