Ever since I can remember, my father has drunk alcohol. In fact, his older brother died from alcoholism when I was around the age of 10 - roughly 7 years ago. This was fine, it was all in relative consideration and I sadly don't particularly love him enough to care.
However, recently - the past year or so - his drinking has gotten worse. He will have a glass of wine in the morning then a beer and/or another glass at lunch. Next he'll have a mid-afternoon drink, with another glass of wine or beer at dinner. Finally he'll have an Irish Coffee and occasionally a peach schnapps before bed. The day drinking doesn't occur while he's at work - unless his boss takes him down the pub - but he makes up for it with an extra glass at home. Also, his boss about 1-3 times a week takes him down the pub for an "off-site meeting" and I'm sure you can wager how much work gets done there verses the amount of drinking.
Due to our lack of a close relationship, I have over the years tended to just avoid him and ignore him. However, recently my mum has been trying to intervene more so than she used to and he is upsetting her greatly. If she attempts to bring up his alcoholism, he will bring up her weight - which is hard for her to control as she has polycystic ovaries - or the fact she earns less money than him. She teaches me at my school so that I have a well-qualified teacher for my subject area and she got pushed out of IT when she had me. He has also just shattered her last vase left from their wedding when he came home in a drunken stupor and tried to blame it on her.
I am sick to death of him treating my mum this way when he has neglected her for most of my life. Furthermore, they nearly got a divorce in the past, so I know they certainly aren't together out of love anymore - just a misplaced sense of stubbornness to not give up. I am planning to confront him over his behavior, but at best I feel I will be shouted I to my room since in his eyes I probably don't have a leg to stand on.
I would like some advice on how to broach the topic with him, in a way that I can come across as calm and mature, even if he decides it is appropriate to insult me. I will say now I have definitely inherited his intolerance of foolishness, which is why I need to know how to not back down without creating a bigger argument than I intended to.
Please note that even if I try to avoid too much confrontation it will occur anyway, so I need to be precise and frame my points in a way he can't do the usual - I have a 1st class PhD and you don't.