"All right, how about this," he tried patiently. "If I can correctly guess the colour of the panties you're wearing today, I get to go home and you get to practice this jutsu on your own."
Sakura's face washed with red instantly, whether from embarrassment or anger or a little of both he couldn't tell, but it was definitely attractive. A moment later, though, she gained control of herself and smirked at him insolently. "Sure, Kakashi-sensei," she said airily. "If you can guess the colour of my panties you can go home—"
"Wonderful," he said happily, and rubbed his hands together. "Let's see..."
"—in a stretcher," she gritted, clenching her fist and swinging at him with all her ridiculous chakra-enhanced strength.
That he managed to dodge at all was due more to his instincts than any conscious awareness of what was going on. Flat on the ground, he watched with bemusement as she overbalanced and sailed over him, landing painfully with her foot in his gut a moment later. The pain was acceptable, though, thanks to the split-second glimpse he'd gotten of the view up her hot-pants.
"Ow," he remarked.
Sakura rocketed back to her feet in fighting position, glaring at him fit to kill him on the spot.
"Green," he said then, knowing that though she couldn't see his smile through the mask, she would see it in his eyes anway. "With little white polka-dots."
She shrieked in fury and tried to hit him again. And missed. And tried again, and missed, and tried again because this was Sakura: stubborn to a fault, with pride trailing behind her like a gigantic kick-me note on her back.
"Mine are pink," he told her calmly while dodging. "With little hearts."
She stopped dead for a full three seconds, then burst out laughing. "You liar."
"I'll prove it," he continued in perfect seriousness. "I'll show you mine if you show me yours... again, that is."
She didn't miss this time, but he didn't try to dodge anyway, only caught her wrist on its way away from his face on the other end of her blow and kissed her wrist.
"Gotcha," he said, and smiled beatifically.
She then wrathfully swore that she would never train with him again, he was a worthless human being and a pervert and ought to fall off a cliff and die painfully with no one there to hold his hand and she definitely wouldn't go to his funeral because he was a jerk and a philanderer and one of these days she was really going to castrate him—
He shut her up with a (mostly) chaste kiss, then vanished while she was too dazed to notice, not stopping until he was a good three miles from her (the limit of her blast radius, as he'd discovered last week).
Kakashi would never get tired of training with Sakura.