We all know that Sasori and Deidara aren't softies. We all know that they kill people for a living. But, for the sake for my story, why don't we assume that they have very thick shells.
Sasori had never really felt comfortable around people, except for his mother, but she's been for years now.
Deidara never trusted people after his mother abandoned him when he was nine.
As an outlet for their anger, they harmed people. It started small, kicking and punching, but it progressed over the years until, in their teenage years, killing people turned into a morbid fantasy. Some people yell when they get mad, they'll just kill you.
Sasori had him pinned to the wall, "Still think you're better now?" The man couldn't breath. "Well? Do you?" His lips were turning blue. "Answer me when I'm talking to you!" Sasori pulled the man away from the wall, setting him back down. The man gasped for breath and a cruel grin spread across his face. He kicked the man, the toe of his boot connecting squarely with the man's nose. Not only did his nose break into his head, the force of the kick propelled his head against the concrete wall, bashing it in. Either way the man was dead. The blood pooled underneath Sasori, he kneeled down and touched the warm stickly fluid, bringing some up to his lips. It tasted of iron.
Deidara didn't understand why these people were so mad. She hadn't done what he told her to do, so he blew her up. Perhaps it was because of the mess that it had been made. He wouldn't have put up with it if it were in his room, but it was a ryokan, and it was their job. "How could you do that to Mrs. Honda! I'll kill you!" The owner said, holding a katana expertly. Deidara, as a reflex, threw a small bit of explosive clay at the man, it exploded when it made contact with his throat. Deidara grinned as the blood hit his face.
"Sasori, here's your new partner." Leader said.
Sasori scowled at the blond youth, thinking about how usless this kid would probably be. Deidara scowled at the thought of having to work with a teenage, being unaware that Sasori was a puppet and therefore twice his age.