>I hope next time i see them in the gym i will tell them "HI.. #blush blush#"

Go for it! Don't just say Hi, ask them what's their training, how regularly do they come, what are their fitness goals, do they have a coach, how did they get into it, do they do other kinds of sports, the merits of this versus that machine/technique/food/training/whathaveyou.

Just talk them to death and extract info on them in the process ^_^