What does "Ddog" mean?
Well may you ask. it means "dog".
Since Mumsnet has the culture of referring to family members as "D" something - DH, DD, DS - there are a lot of people incapable of independent thought who think everyone in their household, man or beast, needs a D to exist.
If they wrote DD you'd assume they're talking about their daughter, but they can't possibly write just "dog". So it's Ddog. And it does my head in because NOTHING is gained by this.