Some parents can't handle not being the centre of attention, but you can't point it out to them because they won't admit it

Your wedding is supposed to be your night. It's one of those (rare) occasions in which the spotlight is on you. Yet some parents still manage to make it about themselves.

They might genuinely feel that they're getting sick, or have intense stomach pain out of the blue, and have to storm out of the party, leaving everyone worried.

Imagine you're so committed to making everything about yourself that you do it unconsciously. I guess you can't blame them, because if they do it unconsciously, they're not doing it on purpose. You can and should get mad at them, though, because they can ruin your night, but in the end, it's because they likely have a very deep psychological wound. Otherwise, why would you do that?

Seeing somebody else shine might trigger feelings of inadequacy for them. They don't consciously want to sabotage your happiness, but they can't tolerate the feelings that arise when somebody else is the center of attention.

Of course, you can't discuss something they aren't even aware of, so you're likely stuck having to process it on your own. If they were aware of this, they would probably manage it in another way, by talking to you or somebody they trust, and trying to resolve their issues. But they can't, and it manifests as sudden stomach aches or itching.  If it really is like this, there is nothing you can do about it.

I was the first in my family to go to college, and when I finally got in, I remember my father looked at me in the eye and said I should go back to school because I was surpassing him. He looked very worried. Instead of being proud, he took it upon himself and saw his own daughter as competence.

Luckily, at that time, I only saw him as a wounded person, and I didn't think too much of it, but he did stuff like that many times years later, and I think it all had to do with his own frustrations.

Anyways, having unresolved psychological issues might explain why you behave in a certain way, but it doesn't excuse you. You still have responsibility for your actions.

That's the most frustrating thing about dealing with people like this: you can understand where their actions come from, but that doesn't mean you should silently accept everything they do. And it certainly doesn't make their behaviour any less hurtful.

When you're dealing with emotionally immature people, you'll end up comforting them for something they did to you, and that's simply not fair. That's why you should be very careful with who you choose to spend your time with, and it doesn't matter if it's family or not.

Understanding someone psychologically doesn't mean you can stop them from ruining your party.

What you can do is uninvite them from the next one! Cheers.