I know this situation, mine frequently goes out without telling me, although I do know he’s going. If I ask him why he doesn’t say goodbye he’ll say that he wouldn’t be long! Because I’ve complained about it for years, he has improved and is more likely to shout ‘Going now’ but not always!
He also frequently leaves the front door open, either when he’s gone out, but more usually on his way back in. Also regularly doesn’t lock up, the back door completely unlocked, and sometimes the front door too! He will never deadlock the doors if he’s leaving alone, but will if I’m with him as I insist or do it myself.
And don’t get me started on mobile phones. He almost never takes his phone with him, never uses it really, only occasionally when he wants to get in touch with someone. The whole family know what he’s like with phones, but he never changes.
However, he’s a good man, will do anything for anyone, adores his family, and has a mountain of good points. So I’m just putting up with his idiosyncrasies.