Nostalgic defending, or defending of any kind. For example, someone will post all the things an average 10 year old has now (phone, Facebook, etc) and say something along the lines of "back in my day, we had to play outside" or the even more tedious and annoying "I had a tamagotchi when I was 10".
Music defending basically consists of people moaning about "our generations" music and how much they hate justin bieber.
Each and every one of them are mouth-breathing scumbags.