mjhjmtu

“What does your dad do at the Ministry of Magic, anyway?”

“He works in the most boring department,” said Ron. “The Misuse of
Muggle Artifacts Office.”

“The what?”

“It's all to do with bewitching things that are Muggle-made, you know,
in case they end up back in a Muggle shop or house. Like, last year,
some old witch died and her tea set was sold to an antiques shop. This
Muggle woman bought it, took it home, and tried to serve her friends
tea in it. It was a nightmare - Dad was working overtime for weeks.”

“What happened?”

“The teapot went berserk and squirted boiling tea all over the place
and one man ended up in the hospital with the sugar tongs clamped to
his nose. Dad was going frantic - it's only him and an old warlock
called Perkins in the office - and they had to do Memory Charms and
all sorts of stuff to cover it up—”

"But your dad ... this car ..." (Harry said)

Fred Laughed. "Yeah, Dad's mad about everything to do with Muggles, our shed's full of Muggle stuff. He takes it apart, puts spells on it and puts it back together again. If he raided our house he'd have to put himself straight under arrest. It drives Mum mad. "

As I understand, Fred is saying that his dad takes Muggle stuff apart, puts spells and puts it back together again and If anyone broke into their house, he would be put straight under arrest. But I don't understand why it drives Mum mad?

Maybe I just got something wrong from the original passage?

-- Excerpted from Harry Potter.

Mum is mad because the shed and house are overflowing with "Muggle stuff." Dad is bringing all his work home, and he's making a big mess with illegal things. It's unkempt and unseemly, and it might be a source of embarrassment to Mum -- not to mention potentially dangerous to anyone who comes in contact with the contraband.