Most people who are "new school" do not understand the older meaning of a ninja flag. It is hard to explain, but Grun did a good job of explaining what the flag system was originally, during ELO days. The old complaints of a ninja flag made much more sense when people complain about ninja flags, because there was nothing anyone, including first place, could do about a ninja flag except unflag.

The current use of these words is closer to "mercy" flagging, or something of the sort. If you are in second all game, and someone who was below you attacks, takes some space, and flags second, he is asking for mercy from 1st place. The game does not immediately end, and you still have a chance to fight and take back second place from this mercy flagger.

I'm not sure if this is a pandemic, or just a few ignorant kdicers, but a ninja flag, in the old sense of the word, is impossible with today's flag system. The only way a ninja flag will work is if 1st place is a player who respects all flags no matter what, which is why respecting flags is an art, and not a science.