In all seriousness, I can feel myself overtrading when my setups are bad, or when I am drilling myself down into a hole; especially off the open. I tend to get this "I can get it back" mentality, which makes me a casino's dream patron. When I look at my account at the EOD and I have executed a ton of round-trips, and still lost big = overtrading. I think one of the main things is not to trade all day, every day. You can burn out, which will definitely lead to losses. A clear head will always prevail. One more thing, trading may be a battle, but it is not a war; you can choose the exit point, take a break, time off, etc. etc.
Overtrading to me is executing trades outside of your strategy for the sake of being in the market (i.e. boredom, recoup losses, etc.) I've actually had more losses from undertrading.
Overtrading: Losing more than winning, over a period of time in which it's reasonable to expect to be winning more than losing. In other words, if you lost 10 times in a row today (or week, month, etc.) and you usually win 6 out of 10, you're probably overtrading. Lack of risk management doesn't seem to qualify as overtrading, although in the literal sense it may be true; over RISKING would be a better way to express that concept.