I didn't go to my 10th, 15th, or 20th. Just got a notice a couple weeks ago about a 25th. Have no intentions of going to it either.
I took ROTC all 3 years of high school and it was my social circle. By the time we were seniors there were only 8 of us who had gone through 3 years, so most of my friends were a grade or 2 behind me.
My main friends wouldn't be at any reunions and the few outside of that circle I have any interest in I have kept up with through the years. I have no interest in knowing what happened to the snobby cliques in my other classes
