As a quick note, we are living with my wife's parents while we save for a house. My mother does not get along with my wife in the least so short of getting an apartment we can't afford right now, we are stuck in the in-laws house.

As the title says, I came home last night from work to find out my wife had let her dad watch our daughter for a short time while she was talking with her mother and sister. My wife decided to check up on our daughter and was able to sneak up on her dad in time to watch him put a beer to his lips and promptly put it to our daughter's.

She quickly removed our daughter after shouting and scolding him. Apparently he was drunk already and they hadn't noticed before giving her to him so she didn't say much else to him. When I got home her parents were already out at a party so I didn't get to talk to them before I went to work early this morning.

Well here I am at work trying to figure out the best course of action from here. I have never liked her father, though I do my best to keep him from that knowledge for my wife's sake. He drinks all the time, not to the point of drunkenness, but has at least a 40oz of Mickey's everyday on the drive home. He frequently drinks and drives in this manner (he never drives my wife or kid anywhere) and to top it off he's a pothead and an occasional coke user.

The family is all well aware of his habits but enables him because he never gets into trouble over it and they grew up with his mood swings and ridiculous overly zealous religious hypocrisy (He is a big church goer and helps at the church all the time). I am vehemently against drugs and alcohol as a rule. I've been drunk once and casually had drinks maybe 4 times in my life. I believe in moderation for alcohol, sure, but his attitude towards being a good catholic while doing drugs and generally being a terrible father disgusts me and this is the final straw.

Worst pf all, he and his wife (who is actually a good person, if ignorant) played off the incident to my wife by saying "Oh it was only one time, he did it to you and your siblings all the time." I am sick of his family coddling him and his behavior with ridiculous excuses like this. Reddit, how should I handle this situation when I get home from work?

Edit: I'm not concerned with the seriousness of the offense, I'm sure no harm was done to my baby. I'm concerned with his disregard for my child and my beliefs and even more that his nonchalant attitude about the situation will become a bigger issue as she gets older and possibly spreads to his other vices.