I think you mean "ditto", which sounds like "diddo" when spoken in an American accent. In a column of figures you can write a ditto mark to say that a figure is the same as the one above. So, by analogy, if somebody makes a remark, and someone else replies "ditto", they mean "same here" or "that's exactly what I would say".

Does anybody remember when teachers gave you handouts that were printed in purple ink (or am I that old)? Those were from ditto machines. Thus, "ditto" means "copy." In slang, "ditto" means, as everyone has been saying, "I agree."

But then again it would be a whole nother thing if the 2nd 'd' was an L.

Ditto. lol

I do not know, I am confused about such words. They like to mix up and then make such inunderstandable words. Why do we need such complicated language? I have no answer.