@.access:
"Fighting you in an imperfect condition is meaningless"
Oh, please, don't -__- don't let Luffy become one of this kind of characters, for god's sake.
I think Smoker's probably the one character that it's okay for Luffy to act this way towards. Previously, Luffy simply couldn't fight Smoker: he was that extremely hard to handle mix of pure strength and a Logia's discorporation abilities that would consume too much time to deal with, and Luffy almost always had more pressing concerns whenever they encountered one another. Even then, that all would hinge on Luffy's ability to pin down a unique weakness a la Crocodile; otherwise it would simply be a curbstomp like Loguetown.
Now, having developed his Haki to the point where Smoker's Logia is not as overwhelming an issue, Luffy's ready and willing to see how they actually match up. But he can't really do that with Smoker trapped in another person's body, hence the postponement.
Smoker's not a villian: his sole purpose is catching people who have good reason to be captured, and that includes Luffy. No one's lives are hanging in the balance, with his defeat being their only hope of salvation. Luffy has no reason to fight him other than as a test of his abilities or to protect his crew, and the Strawhats have a decent record of getting away from their pursuers.
Since Luffy's only reason to fight him (unless/until he captures some of his crew) is to finally see how they match up head-to-head, why would he want to fight Smoker in Tashigi's body, where he (Luffy) would be at an inherit advantage?