"Perfect" is too strong an hypothesis, but none of those behaviors are irrational per se.
People would rather be fit than overweight, but that's not the choice on the table. You can either make sacrifices now to be fit X time from now, or eat that ice cream and suffer later. The rational choice depends on the relative value you put on those things (and your discount rate, if you want to get really technical).
Taking the "wrong" side of the tradeoff could certainly qualify as being stupid, and as you note all of us would turn out to be plenty stupid if we started rigorously analyzing our choices, but this is a matter of people claiming to have preferences they don't actually have, as proven by the only thing that matters: their behavior.
However, you could also choose to believe their regrets, when they look back on their own choices and say that the pleasure than they gained from them did not repay the misery they suffered because of them.
If you choose to disbelieve their regrets, then maybe you would agree to label their regrets as stupid?
- I now have information I did not have at the time I made a choice that binds me now.
- I changed my mind.
Whether I believe it or not makes no difference because it contains no information.
As an aside: none of this is supposed to invalidate the experience of people having regrets, or struggling with addictions. If I see a friend getting drunk every night I won't go "ah, yes, they are correctly maximizing their utility according to their own discount rate and inter-temporal budget constraints". They are separate conversations, though, and we can have the kind of conversation where I help you solve problems or the kind of conversation where I just listen to you. They don't tend to mix well.
> they’re intelligent when it comes to their own lives and the areas they work and spend time in
Are people likely to get fat when they have easy access to a bunch of cheap food that is optimized for overconsumption?
Are kids likely to skip all necessary and/or useful preparation for adulthood, given the opportunity to watch porn or TikTok instead?
Are people likely to believe pseudoscience influencers over mainstream medical advice?
If you dig into these examples, you can explain each of them in more specific and illuminating ways. "Stupid" is just shorthand for the fact that we're not perfect rational optimizers of anything, including our own happiness.
(I think people twist themselves into knots trying to avoid using pejorative words like "stupid." I appreciate the good intentions, but I don't think it's necessary. I'm stupid a lot in my own life. Everybody is stupid sometimes. We're human beings.)