The clip comes from Team Fortress 2 and features Heavy, the Russian minigun class voiced for the game. The full line is addressed to the Medic, his usual partner, but editors isolated just the final confused sound for fan videos and soundboard use. That kind of tiny voice edit became common in TF2 meme culture, where single Heavy, Scout and Spy lines are looped as reactions separate from gameplay footage.
About this sound
Short confused grunt from Heavy in Team Fortress 2, cut from we go together doctor. Used for dumbfounded reactions and quick meme edits.
This is a very short, flat grunt from Heavy that sounds like a bewildered duh. It is clipped so tight that only the confused tail of his sentence remains, leaving a blunt, slightly annoyed noise. That emptiness is the joke, making anyone it is placed over seem instantly lost, slow to catch on, or caught without an answer.