RORY: When did you see me with Dean?
JESS: At that stupid summer insanity plea the town put on.
An insanity plea, otherwise known as a mental disorder defence, is an argument put forward during a criminal trial that the defendant is not guilty for their crimes due to a psychiatric disease at the time the crime was committed. Using this as a defence goes back in law to the very beginnings of recorded history, and although it’s popular in fiction, it’s rare in the US – used in about 1% of cases, and then, only successful about a quarter of the time. The person who succeeds in winning their case this way will usually have to undergo psychiatric treatment in an institution instead of a prison sentence, or as part of their prison sentence.