Is it safe to touch 1000 Volts DC at 1 mA of constant current? 0.1 mA? 0.01 mA?
Unless we're talking about being cooked alive, no, it's really not the Watt that kills you. It's the current flowing through your body, making muscles contract through electrochemical reactions, and nerves disfunctional.

To achieve a dangerous current, due to the resistance of skin, your body and your contact to whatever closes the circuit with the source of electricity, you need sufficient voltage. And, of course, as you noticed, even if you have a voltage source, it must be able to source that amount of current without breaking down.

So, your wattage considerations are plain wrong. Wattage is a side effect, but the power spent in the human body has nothing to do with danger. If your 10 kV voltage source can only source 1 mA, it is way safer than a 100 V supply that can supply 100 mA.

Soooo, let's have a graphic:



From this article.

In short: don't ever conduct more than 10 mA through a human body.