Expressing frustration at the realization that things have turned out badly or not as planned, or that one has just said or done something foolish. Also (usu. mildly derogatory): implying that another person has said or done something foolish.There are a lot of Homer moments when you'll just roll on the floor laughing as he says d'oh. I'm sure you'll laugh just as hard when he says it in Japanese.
The video above is part of Thirty Minutes Over Tokyo, where the Simpsons family spend their vacation in Japan. Naturally the father and son duo, Homer and Bart, instigate trouble which consequently lead them to spend time in jail where they learn Japanese culture. As he shows off what he learned to Lisa by making an origami crane out of their last one-million yen bill, the wind blows it off out of reach. This causes him to d'oh in Japanese.
What Homer really said was shimatta-baka-ni which can be roughly translated as "damn it stupidly". The actual translation of d'oh in Japanese however is dottsu, written in hiragana as どっ! Not convinced? Here's proof.