Is it weird for a guy to hug someone else? Like, if one of my acquaintances is really sad and I want to hug them, can I? Or is it more acceptable for a woman to do so?

It depends on the person and the type of relationship you have with them, but generally this should be avoided with mere acquaintances. Many men are uncomfortable with getting that kind of affection from other men. Meanwhile, women might see it as a crossing of boundaries. Both genders can be uncomfortable with the same thing from a female acquaintance as well, though the discomfort level may be lower due to women generally being expected to be more friendly and nurturing than men (so it's more in line with gender norms and less potentially weird/suspicious).