If you spill something on it that stains (eg coffee), you put on another shirt and because it looks the same, people will think you have an awesome washing machine so burglars will come and try to steal it and you'll catch them and get lots of money to buy more of the same shirts!
L could tell that this coffee was going to be a good one. A very good one. Just by looking at the shade of brown the detective could tell. But it wasn't ready yet, just a few more sugars.
'L do you mind if I-' Light's hand knocked the cup and all the contents spilt all over L's white shirt.
'S-sorry Ryuzaki...' L stared at him with wide, saddened eyes.
'That was going to be a good coffee.' L sighed. Standing up, he gave Light another sad look.
'I'll put this in the wash.' Murmured L. Light laughed. There was no way that a washing machine could get rid of a stain like that.
Minutes later, L came back into the room with what seemed to be the same shirt, but with out the stain.
Burglar Bill was looking for a nice doughnut to steal, preferably one with lots of sprinkles.
'You must have one great washing machine.'
What was that? A washing machine eh? Bill needed one of those.
'Got rid of a stain like that!'
It was coming from that window up there!
'I was sure it would never come out!'
Now Bill was interested. He needed a plan
He really needed to lay off on those doughnuts. That window had been a tight squeeze. Bill had made a lot of noise too, but luckily everyone was asleep. Now all he needed to do was find something that looked like a washing machine, grab it, and climb back out the window. The thing was, it was pitch black. So no sign of a washing machine.
He fumbled round, feeling the walls in hope of finding a light switch. And he did. Light filled the room and tears filled Bill's eyes as he saw what he had been searching for. Although it was a cardboard box with glitter on it and buttons drawn on in orange felt tip, Bill knew that this was it.
After he pulled himself back together again, he reached out and touched it. To his surprise, the box ripped itself open. L's head appeared, and so did his finger of doom, which he pointed at Bill.
'What are you doing?'
'You were trying to steal this weren't you?'
Without waiting for a reply he lifted his head and screamed, 'EVERYONE WAKE UP AND GET YOUR ORANGE FINGERNAILS OVER HERE! WE FOUND ONE!!! Would you like some cake?'
Doors burst open all around them and men, all in teletubbie pyjamas stormed in.
'We've got ya' now sunshine.' said Chief Yagami, putting handcuffs on Bill.
'I think I need a reward.' said L
'Ah yes. Here you are.' L was given ¬£100. L turned to Watari
'Can you take this and buy some more shirts for me? Make sure they all look the same as this one.'
The next day, Burglar Bill died of a sudden heart attack. L's suspicions of Light went up by 10%.