It's not just girls. Guys cry, too. I laugh when it's not severe pain. I promise if a guy broke his leg he'd be crying just as hard as any girl would. It's more of a pride thing. Guys are like "oh man, I don't wanna cry and make them think I'm a baby."
Yep, women aren't afraid or ashamed to show pain, sorrow, or other icky stuff. We just let it out. -- That's why we live longer! Muhahahaha ! Guys are trained to be stoic. Usually by other men who learned to hold it in when they were kids, and on back in time to caveman days or earlier. Probably some cave woman got tired of hearing the men whine and told them to suck it in, so they did. -- And so they hold it in till veins pop. Pop! Thump! (So sad) It's a plot that goes back to cavemen days, but now that I've spilled the beans, I feel better.