Man: "What are you going to do with all those muscles? Beat up the boys?"
Me: "Yup."
Man: "Well then, stay away from me.
Is it any surprise that women want to go to their own gym. Here's a good rule: unless women indicate otherwise, assume that they're in the gym to work out, not to be hit on, and that they don't need your opinion of their workout plan.
On the other hand--speaking of equilibrium effects--the success of women-only gyms likely increases the fraction of women at mixed gyms who are receptive to male come-ons. Who knows--if Curves and its ilk really take off, your advice to men at mixed gyms might cease to apply....