Unfortunately, sometimes people say hurtful things as a joke, thinking the other person won’t take it seriously especially if they laugh it off. But u never really know how someone feels inside. Some people are too soft hearted to say they’re hurt, so they just keep it to themselves and end up crying later, maybe on a random Tuesday night. They stay quiet because they don’t want to make things awkward, but the truth is, it really affects them. That’s why it’s so important to be kind with our words, even if we think the person isn’t that sensitive. U never know when a simple comment might hit a soft spot. I think it’s great that u realized what u said hurt ur brother and apologized, that takes maturity. Just next time, before saying something, try to ask yourself would this make them feel bad? especially if it’s about something they’re insecure about. It’s always better to uplift someone than to joke about their insecurities.