I've said this on predictions/discussion. I have no problem with Konohamaru using Rasengan. I think it's quite fair for him to use it, and it doesn't spoil the jutsu. It doesn't make Naruto look bad.
Naruto learned in a week or so can't remember.
Konohamaru took almost 3 (time skip included) years to get that little Rasengan. It took the Fourth four years to invent it and perfect it. Konohamaru knew what he had to do to train the technique and it took him 3 years. How does that make Naruto look bad if he only took a week (Tsunade bet)?
I think some people are over-reacting on this matter. Naruto at his age also took down a lot of enemies that at the beginning seemed impossible for him to fight (Kabuto etc...) .
Now Konohamaru hits that particular Pain body (used for interrogation and not fighting), with a tennis-ball-sized Rasengan, made with a clone, that didn't even kill him and some people start whining that he shouldn't have it.
Plus, i'm sure that he didn't defeat it, that Pain body will stand up in the next chapter.
Don't underestimate Konohamaru he is the 3rd's grandson, and had the best Genin sensei, Ebisu.
He is supposed to be similar to Naruto (Hokage descendance, pervs, Hyperactive etc...). It only makes sense for them to have similar jutsus.
Stop talking bad about Kishi for this...
Cheers
