Not sure how to approach this question so please bear with me.
Every member of my family, including me, has a problem with my father's behaviour. I am trying to find a way to solve it.
Simply put, my father comes home after work and immediately reaches for the beer. He drinks 5-6 cans a night. He gets drunk, not a massive amount, but enough that his behaviour changes. In fact, I think he enters this behavioural mode automatically before he even starts drinking.
What is this behaviour? Well, he interrupts and critises people on everthing they say or do. I mean everything. He mostly does it to my mother - he undermines everything she says and it is affect me since I can't even have a conversation with her without him saying something about every single thing she has to say. It gets to the point where my blood boils but no matter how much I or my mother tell him to stop being irritating he doesn't seem to acknowledge it. I can't stress enough how demoralising it is to have someone put down everything you say constantly.
When we confront him about it, which is usually when he is in this state (i.e.: after he's had a few beers) he becomes very defensive. He turns every genuine argument we have into a joke, behaves like a child and eventually gets angry and starts spouting some incomprehensible or illogical sentences in an attempt to change the topic. For example:
Me: Dad, your behaviour is annoying. We've told you numerous times to stop yet you continue.
Dad: Oh it's just a joke, what's life without jokes. (immediately deflects)
Me: I am being serious here, you do this all the time, it is irritating, offensive and you cannot treat me or mother like this. We can't say a single world without your needless comments interrupting us.
Dad: Oh so I'm not allowed to have an opinion? I am not allowed to say anything? (tries to imply he is a victim)
This is how it starts... He fails to acknowledge what he does to us. He starts acting very childish, almost as if he's giddy. Anything we say, no matter how logical and earnest, he dismisses with a deflection or some twisted logic.
It's easy to see it's near impossible arguing with him or trying to change his view while he is in this state. I have spoken with him about his drinking problem but he fails to see it as a problem. For him it's just a way to unwind after work and he fails to notice his change in behaviour. He refuses to even contemplate the idea that these beers might be getting him drunk.
The worst part is that this behaviour mode, as I said earlier, has been happening for so long now that he often enters it when he knows it is time to relax (i.e.: no alcohol involved to begin with). This includes going out on weekends, making public events with him unbearable.
How can I handle this behaviour? It is impossible to talk sense into someone who is so stubborn and childish.