For the electrical gurus excepting Dan
I quess.
Well think what you want about Dan, but he won't steer you wrong. By asking this question very question you are exhibiting a deficiency in automotive DC wiring methods. Wire up the horn anyway you want, its your car.
My 2 cents for anyone reading this thread:
Wiring a push button direct between battery and horn will result in a melted push button.
The problem is most push buttons are not rated for much amperage, cannot provide positive tight contact sufficient to keep switch closed without arcing. You have to employ a relay in the circuit to handle the high current draw that a horn requires which can be safely triggered by a push button switch.