[quote="Regulus"]
But, I think Simba had to be aggressive.[/quote]
Also, I have no doubt that Simba knew that he wasn't much good in fighting. What do you do when you are outclassed? Bluff. Simba had to try and convince Scar, an underweight and weak lion, to go down without a fight and leave, because against Simba, Scar still has a very serious chance of winning. Obviously, asking Scar to simply leave wouldn't work, so Simba had to compensate for his lack of skill with plenty of bravado.
I think it only worked against Scar, who being the weak lion he is, and not knowing Simba's skill, has no choice but to call on Simba and only fight when cornered. I have no doubt that a lion like Mufasa, if going up against Simba, would simply charge and get it over with.