What does DG do that makes him a douche? I honestly don't know because I've never really cared about him or POS enough to read anything about what he says or does.
Well, he has a very 'interesting' look on his own music. I'm not saying that a musician shouldn't be proud about their work, but he sometimes come off as a douché in the way he says certain things. For example, in an interview he was asked about their album "One Hour By the Concrete Lake", to which he said "It's probably my least favorite POS-album, but still more original then most music out there". We also have that interview when he said something like "the progressive metal scene hasn't changed in 15 years", which is funny considering his band is very much a part of that scene.
When PoS was in a music-contest here in Sweden a few years ago, and Road Salt didn't win it all, DG said stuff like "people here dont understand quality" and "the competition was rigged".
It's his sense of humour I guess. Some find it funny, some find it douchey, I think it's a little bit of both. But across several interviews I've seen, he has very high thoughts of his own music, but often talks down a lot of other artists.