I am made entirely of FAIL!
Draco didn't understand why on earth he would need to cast a Patronus. It wasn't as if he didn't know how to properly hex a message, how to be private. Hadn't he done enough of that to prove himself?
Still, he found himself uttering the embarrassing password to the Headmaster's office, and coming in when he was asked.
"Headmaster," he said, politely snide, as he came into the office.