Someone I was pretty good friends with in college does this on a regular basis. He posts links and videos with inflammatory comments about stupid liberals and such, and at least once he's publicly called me and a couple others out. He routinely baits his Democrat and liberal friends.

It's gotten to the point where I just skip over his newsfeed items because he makes me so angry. I've considered blocking him, but he's not an all-around bad guy and I still have fond memories of good times in school. There's a line, and he's put his toes up to it a couple times but hasn't yet crossed it.
http://unpavedpath.blogspot.com/