Disclaimer: I do not own Naruto, or any other characters mentioned.
Scaredy Cat
Naruto did not enjoy being scared. He'd spent the majority of his childhood that way, terrified that people would go from shoving and screaming at him, to that they would hit him and not stop. Naruto had not really wanted to die, even though he hadn't really had anything to live for.
And therefore by connection, Naruto did not really like Uchiha Itachi either. Of course this was partly because the missing-nin had driven Sasuke to the point of insanity, but Naruto was still not exactly happy with Sasuke right now, and felt it a bit difficult to feel sympathy towards him. The bastard had made Sakura-chan cry, after all.
But even from the first time he had seen Itachi he had felt that Itachi would be the death of him. Not even the shark-man who had stood next to Itachi, and had been so interested in cutting him up into pieces, had seemed as dangerous. It had been clear even to Naruto that Itachi was the one in control.
So, when the pervert asked him why the hell he wouldn't stop training, even when his body was one large bruise and his hands were covered in chakra burns, he plastered on a grin and said he had to be strong enough to get Sasuke back. And while that was only a part of the reason, not all of it, it was enough for the pervert to go back to his 'research', and leave Naruto to struggle his way through complicated scrolls and techniques in peace.
Because Naruto had never been one to run away from fear, and he never wanted anyone to see just how scared he was. Sasuke calling him a scaredy-cat had been a factor into that.
And he might feel bad when he never told Jiraiya the complete truth, but Naruto would do anything to be strong enough to face this fear.
He really didn't want to die, after all.