Harry, Ron, and Hermione do not have their wands when they encounter
Malfoy and his two brainless bodyguards. Seeing vulnerability he starts
to threaten and insult them. Harry calmly walks forward until he's just
inches from Malfoy's face and with an air of quite confidence says:
"When we were in the first year you challenged me to a wizard's duel,
but you never showed up Malfoy. Let's finish it, right here right now."
Malfoy was so surprised by this remark he didn't say anything.
"Why do you hesitate Malfoy, it's a perfect time for you, I'm
completely defenseless. Well ., not completely, because you see, SOME
CURSES NEED NO WAND, or hasn't your little buddy Tommy Riddle taught
you that yet."
Looking even paler than normal Malfoy said "You're bluffing".
In a low menacing voice Harry growled "Well maybe I am and maybe I'm
not, but seeing as how I'm talking about the guillotinious curse, one
of the most powerful in the world that would slice your head clean off
you have to ask yourself one question. Do you feel lucky today?"
Malfoy, his eyes the size of saucers was speechless. With a evil grin
on his face that made him look just a bit insane Harry leaned even
closer, looked him straight in the eye, and whispered very slowly "Well
do you punk?"
Paralyzed with indecision Malfoy looked down at his wand just inches
from his trembling hand. Then in a voice so loud it almost sounded like
it had been magically amplified Harry shouted into Malfoy's ear
"DO IT! MAKE MY DAY!"
Malfoy staggered back his ears ringing with pain, and then without
another word he turned around and walked away.

As she watched them go Hermione muttered under her breath
"Dirty Harry".
"What?" said Ron in surprise "Harry's not dirty."
"Brilliant!" Said Hermione "You really should get an Oscar for that
Harry"
"Who's Oscar?" said Ron.
"Thanks Hermione" said Harry quietly still looking at Malfoy's back "If
this wizard thing doesn't work out maybe I could get a job with
Mr. Eastwood".
"Will somebody please tell me who Oscar Eastwood is!" Said Ron getting
exasperated.
"Clint" said Harry in a monotone, his attention still on the tiny
figure of Malfoy retreating in the distance.
"What!?" said Ron now completely confused.
Then Hermione and Harry started to laugh.
"Huh?" said Ron "What's funny?" But they were laughing too hard to
answer.
Ron looked at one then the other and shook his head "You've both gone
mental"