How to tell a girl that you want only to stay as friends?

I lol'd, very hard. No, I don't talk about Smash all the time irl, lol. . . Actually, I was talking to her about how I enjoyed to exercise by running up hills and sh`t, and she was like "Oh really? That's pretty cool . ." and I was like "Not really, I don't think it's anything huge. I just enjoy running and jogging, haha.", and blah blah blah. She brings up some rather obvious hints at times when we speak, but it's not as obvious as that other chick last month that flirted with me everywhere. <_<