Ilka Tuk Tak

Ilka Tuk Tak is the most excessively overused expression in the Orcish language, featuring in just about every second Orcish sentence. Long time presumed a swearword, it is now theorized that, due to the limited expressiveness of the orc facial features (in no small part to be blamed on the excessively unwieldy cheek-mouths and prominent snouts), Ilka Tuk Tak is an auditory indication that the speaker is undergoing an emotional state of surprise or disbelief. The reason it isn't translated is simply because there isn't an equivilant word or phrase in human dialects.

Alternately, the entire Orcish race suffers from a particularly nasty case of Tourette's Syndrome.

Or the Orcs could just speak Scots, where Ilka Tuk Tak means "Gather each thorn," which gives a culturally appropriate meaning and sets it as a demeaning task rendering it an idiomatic equivalent to "Oh, boop me."