Please, don't jump the gun and go around blocking people that haven't done anything to you on this site yet!
You follow him. (Ha! You didn't expect it, did you? ) Apparently there's this option. Go to :
Just hover your cursor over that area. Apparently you can block a user you're following.
*Stipulation - I haven't tried it yet. Once I find a willing victim *coughs* volunteer I will know.
*I'm also still not clear on what blocking someone does. Any volunteers?