Excuses my Son used last year.
(1) It's against my religion to do any homework.
(2) I lost it fighting this kid who said you weren't the best teacher in the school.
(3) I was abducted by green-skinned, three eyed, pig-snouted space aliens and they incinerated my homework with their death rays.
(4) I felt it wasn't challenging enough.
(5) My parents were sick, and unable to do my homework last night. Don't worry, they have been suitably punished.