I generally don't believe that giving people the third degree is polite at all. But at the same time, if you're a person who's prone to lying and exaggeration, you only have yourself to blame if people start to question everything you say.
My mother is very prone to exaggeration and making things up to fit her convenience. She's especially prone to making up conversations and, when you call her out on it, she'll say "Okay, he/she didn't say that, but they wanted to. It's the same thing!."
Well, no, it's not the same thing. When I was younger I'd sometimes get dragged to things I didn't want to go to because "They invited you specially! They'll be so offended!" Then, when I got there, I'd realize that my invitation existed only in my mother's head. Her defense? "Well, I thought they meant to invite you. How was I supposed to know it was adults only?" AGH!
And now that she's gotten older and her health has gotten frailer, I get to hear worry-inducing stories of heart palpitations and tumorous lumps and various terrible and fatal diseases she's sure she's got. These terrible illnesses especially occur around holidays and when I enforce boundaries. There's usually just enough truth in her exaggerations that I can't dismiss it all out of hand. She'll actually save up health scares, rather than tell me at the time, so that she can bring them up later when she wants to manipulate me. I can get the straight truth from my dad but, if he's not around, then yes, I'll grill my mother to get to the actual truth of the matter.
I guess the point I'm trying to make is that while the OP's father's behaviour can seem pretty harsh to an outsider, if you live with a compulsive exaggerator/hypochondriac you get pretty good at telling when you're being played. Especially when, as seems to be the case here, the illness follows a convenient and predictable pattern.