i had a stalker a few years ago that would just come up to me and start some random, 1-sided conversation about things that had nothing to do with the gym or working out. Usually it was something political or religious. just weird. I tried the ignoring thing, and that simply didnt work.
So finally, i snapped. i had drank a full bottle of Redline on the way to the gym, had a crappy day at the office, and all i wanted to do was lift. And Random Conversation Dude walks up and starts. I looked him in the eye, and said, rather loudly, "Do I even know you?" You coulda heard a pin drop in the gym. He paused, and as he started to form his first word, I looked him in the eye again and I said "Do not even think about speaking to me again." i turned around, and went back to my workout.
He's still there, but he hasn't spoken to me since. I gained about 5 friends in the gym that night. Apparently, he had driven just about everyone else nuts in the gym too, and no one would say anything to him.