Most untrustworthy race in the galaxy?

Kirk: "How do I know you'll keep your word?"

Khan "I've give you no word to keep."

Kirk: "I see your point."

 

Not necessarily, no. See, with humans, you don't know what you're getting. With Pakleds, Romulans, Borg, Klingons, etc., you can bet that treachery may be a serious part of their culture, but with humans? Hell, no. We'll smile, shake your hand, share our noble sentiments, invite you into our homes, make you a part of the family, and all the while we could be taking everything you hold dear, or preparing to end your life. No one is more treacherous than a human, we're just very good at hiding it.

 

Any Admiral in Starfleet.

 

^ Except Forrest (either version).

 

The soul eating Devidians, or Fajio with that nasty disruptor of his. The folks who left Armus behind maybe.