Why Can't We Be Friends?
For many people, time at the gym is about more than just getting healthy and strong. For those people, time at the gym is some of their only "me" time. It is the time that the guy who spurned you spends AWAY from the troubles of his world. When you asked him for a spot it may have reminded him of the wife he's at the gym to avoid!
That, or he's just a jerk.
In either case, what you can do in this situation is ask if he needs help with any lifts, and suggest that after that he could spot you! I have found, by experience, that this strategy works very well.