When did "Average" become "Bad"?

I went and saw Daft Punk the other night, and said online that it was pretty average.

I enjoyed their music, but thought the rest of the night was pretty average. There was a lot more they could have done with the set up to make it really outstanding, like having screens to show the Daft Punk guys pushing the buttons in the pyramid.

Now I've been flamed for saying this, and people have assumed I hated it.

I didn't hate it. I never said I hated it - in fact I'm glad I went... however, because I called it average there's all this hate being directed to me.

Its the same when I review computer games.

If I say a game is average, and give it a score of 6 or 7, people assume that means I am saying the game is bad.

It's not bad, it's just not great. In other words - Average.

So, when did "average" come to mean "bad" in most peoples mind?