You don't care? Whoa...not a good place to go. This is a tense situation and you need to place yourself in his shoes.
As I said before becoming postive proactive and not negative war here is the way to go.
You are at a fork in the road and building a relationship with this person is the goal, not tearing it down.
Yes he was a JERK of the highest order. If you really want to go over there and resolve it, go over there yourself. Do not send your DH. That is how things begin to get blown out of proportion. Take him out to lunch to talk about it.
In other words go "Dr. Phil" on him and not "Jerry Springer".
Exactly. Everyone agrees the Dad was way out of line. And it is wonderful that you are able and willing to be there for his daughter. It truly is.
However, in almost every one of your posts you have referenced everything that you've done for his daughter and everything that he hasn't.
I have seen this before and trust me when I tell you this is not the time to get into a pissing contest with the Dad over who is the better parent. In the long run, it is not good for you, not good for your son, his GF and most of all, not good for your grandchild. When it's all said and done, nobody wins.
He was wrong, you are angry and you have a right to be. Cool down, and then calmly talk to the Dad and find out what's really going on here. Because it's more than just the fact that she didn't come home after one night.
Sometimes, being the better parent means being the bigger person. It goes a long way toward building relationships, and like it or not, all of your lives are now going to be intertwined forever from here on out.