High School Reunion was on the WB for three seasons a few years back. You can even see the old forums on this site still. I remember the VH1 special that mentioned and "exposed" it, there were some people from the same high school from different graduation years or something, that's all. It wasn't "fake."
Now it's on TVLand but it's a 20 year reunion now, and I think it's pretty good. Lots of drama, and although the little high school names attached to everyone are kind of cheesy ("The Jock," "The Geek") it's definitely real. There's one poor guy Mike there who's ex-wife slept with his best friend and they both showed up and the poor guy is miserable! Good stuff.