It's so hot in this weather … will it make people laugh when they go out in vest shorts and flip-flops?

No, don't worry, if it's a girl, no one will laugh. If a boy dresses like this, most people won't care what you wear unless someone who loves neatness will accuse you. As long as it's not naked, I'll wear it like this. I don't care as long as I don't go to important occasions. As long as I am cool and comfortable, there are still many people with ordinary vests, shorts and flip-flops.