An excuse for everything.
1) Teacher: "Why were you late Jimmy?
Jimmy: "My blood sugar was low!"
2) Teacher: "Jimmy, you know, that you're only permitted one dessert!"
Jimmy: "Oh my blood sugar is low."
Teacher: "Oh OK then have a third one too!"
3) Principal: "Why did you go home after the second period, Jimmy?"
Jimmy: "My blood sugar was high!"
Principal: "Oh. Just forget, that you were even here!"
Diabetes. (It would not let me post the example without writing it)