PCIe connectors are supposed to be keyed to fit one way...unless, of course, it's forced in.
Well, I could easyly plug them in upside down and burn out S2's stock PSU. It's being repaired now. I never thought that this is possible to do with PCI-E connectors. 
Pics or it didn't happen.
PCI-e power connectors are keyed so they only fit one way. If it was possible, we'd have read dozens of stories just like this over the past year.
Unless you have gorilla-strength and are able to force square pegs into round holes, then it's impossible.