I've got an Easter egg in my Foundry mission where an acting ensign in engineering has done something stupid involving green lights and a plasma plume, the chief engineer is standing there yelling at him, and there's a Starfleet Klingon ensign on the second floor pointing-and-laughing. I want to know how to say, "What an idiot!" in Klingonese for the Klingon's dialog bubble.
They don't have "hello" either. According to a book on imaginary languages (including Klingon, JRR Tolkien's Middle Earth languages, loglan, etc.), I think the closest approximation is: "If something" (or someone) "is in your way, knock it aside."
yIntagh is actually the most literal translation of the English word "idiot."
nuq toDSaH literally means "You wimp" or "You wuss" (only more so)
petaQ has no direct English translation, but it's a semi-curse word that falls in somewhere between "bastard" and "@$$hole."
For "hello" - if approaching someone and you want to get their attention, you grunt (if they are an inferior) or say "Sir" (qaH) if they are a superior. The response when being approached is always nuqneH? ("What do you want?")
And yeah, Bing's tlhingan Hol translator sucks out loud. But translating between the latinized Klingon and pIqaD (Klingon script) works like a charm.
When I come across a Klingon word I don't know or need to translate something into Klingon, I use either this site or this one. Constructing sentences is what gets people thrown for a loop though. Using suffixes Klingons can actually condense an entire phrase or even a sentence into a single word, and their sentence structure is very alien (although it follows for the most part a strict rule of object-verb-subject that makes perfect sense once you understand it.)
"A Gorn walks down the street in that hat, people know he's not afraid of anything."