Safe order for three signals GND TX RX

[alank2]

I need a 3 pin header and I don't think there is any standard for it, but I could be wrong.  What is the best order to keep someone from causing any damage/trouble by reversing the connector?

TX is an output (driven output high/low)
RX is an input (HiZ)

This keeps the output in the middle...

GND TX RX

[KL27x]

Putting the Tx in the center is fine, but isn't the Rx connected to a Tx pin on the other side? You would end up with a short between a Tx and a GND or other Tx any way you slice it, no?

If you want to use a reversible 3 pin connector, it probably doesn't matter in the sense that it probably won't cause permanent damage. But you could check the datasheets. Or you could put a 10R resistor on your Tx and Rx pins.

Safest is to wire it to a 4 pin header. Cut off one of the pins on the male side and plug the hole on the female side with hot snot or epoxy.

[Monkeh]

Both your TX and RX should be able to survive being shorted high, low, preferably somewhere above high (like 5V), and ESD from probing fingers.

Sort that out and you'll not have to worry about the order.

[xrunner]

Safest is to wire it to a 4 pin header. Cut off one of the pins on the male side and plug the hole on the female side with hot snot or epoxy.

That's what I was going to say. 

[Doctorandus_P]

From an ESD point of view it is very preferable to make the GND connection first.
When using standard 0.1" connectors you can push the GND pin out a bit, so it makes first contact.

Putting in small series resistors help a lot in preventing ESD damage and also help in preventing damage from short circuits. But they may limit the baudrate, especially on long cables.

With a 5 pin connector you can have 2 GND pins on the outside. Then two pis for Rx or Tx, and a single pin in the middle. This would make your connector reversible.
I suggest the GND pins on the outside, because it is likely the connector will be first inserted under a slight angle and the outside pins make first contact then.