The lollypop.
Naruto started it really.
The lollipops for correctly done mission reports for Genin that is.
Iruka had of course resorted to old fashion bribery at times while teaching his classes and Naruto saw no reason why it had to stop outside the class room.
Iruka, sick of the argument had (using petty cash) purchased several ramen flavored lollipops to be handed over when Naruto handed in a correct report, and Iruka meant correct. No spelling mistakes, no smudges and all details included in the right sections.
Naruto got a lollipop about one in every five reports. (When he really needed the sugar after a mission). Of course this set off the other Genin who also found report writing unrewarding and so more lollipops was bought.
The office Chunin thought it all very silly but put up with it for the clean and therefore easy to file reports.
Then Gai decided he needed to improve his report writing and demanded that Iruka give him a lollipop when ever he gave in an excellent report.
Not that hard since Gai was a perfect report writer as it was, so a box of bright green lollipops were purchased just for him, much to his teams chagrin.
Well, Neji's any way; Tenten thought it was cute and way less embarrassing than some of the things their Sensei did, while Lee wanted to write up the reports himself for extra training. Trouble then started because the rest of the Jonin started wanting lollipops too, but none of them wanted to do a proper report to get one.
Now Iruka really put his foot down on this one. Genin and Chunin were handing in good reports (except when team members were dead, dieing or hospitalized, bad reports then just weren't an issue) and the Jonin were not. So unless the Jonin lifted their game they weren't getting any lollipops.
Iruka booby trapped the box and cupboard where they were kept just to be sure. The Hokage, sick of all the arguing and screams from the aforementioned cupboard, made it official – Clean and tidy report means 1 lollipop – end of story.
Soon all the Jonin including the extra scary ones had all fallen into line. Yes the more paranoid ones did take the lollipops apart and test them for poisons etc, but on the whole every one was happy.
Save one, Kakashi Haytae refused to hand in an clean tidy and accurate report on anything but the most the most important mission and even then he'd deliberately stop, put ink on his thumb and smear down the margin of the report before handing it over to Iruka. Who glared but did nothing, until the day, the wall of the mission office received a new decoration.
Directly behind Iruka's desk a wooden display box with a glass front was fixed. Covered in seals on the outside the inside was lined with royal blue velvet and on the velvet rested a large Lollipop. It was beautifully handmade, about 10cm in diameter with different flavors for each different color. But the picse de resistance was the two intricate figures inlaid upon it.
Most of the Ninja in the office took one look and grinned.
Gemna and the Hokage started a betting pool. Iruka just looked serene and waited. Kakashi turned up in the late afternoon and wondered why the mission room was so crowded before slouching up to desk and handing over a sloppy report.
Then his eyes found the display, his heart stopped and his mouth started to water. Before him in all its glory was an Ichi Ichi paradise theme lollipop. He swallowed, and then swallowed again before hearing Iruka calling his name. "This reported is not lollipop standard" were the words that shattered his world.
Kakashi looked at the challenge in Iruka's eyes and smiled before dragging himself out of the mission's office.
The next year and 3 months were a contest of wills between Kakashi and Iruka. At first Kakshi just tried to steal the lollipop but it was too well protected. Then he tried the steal the display case, the piece of wall it was on and lastly that whole section of the office, but Iruka had been very though in his security. These attempts were intersperse with break-ins to Iruka's apartment, classroom and desk, kidnap attempts and various attempts with truth serum in food and drink for Iruka.
Who countered with booby traps (bees, various mild poisons, really stingy whips and mousetrap like devices) cleaning duty, a thorough knowledge of escapology and an unbelievable immunity to truth serums.
Finally for the first time in his (non mission) life Kakashi admitted defeat and wrote report that was a thing of clerical delight. It was clean, accurate and detailed.
He grudgingly slouched into the mission office and slid the report across Iruka's desk.
Iruka took 10 minutes to go over it and then graciously stamped it and filed it.
With beatific smile Iruka then released the seals on the display box (No Kakashi didn't see how, he was staring at the floor) and handed over the lollipop.
Kakashi mustered up what dignity he could as he walked away with his prize to the catcalls and whistles of his fellow Jonin.
The next Time Kakashi went put in a report he saw the lollipop had been replaced by his beautiful report neatly framed with the caption 'Winner of the sucker award'.