Why is inconsiderate behavior so common?

What the heading said. Walked into class today, my friend and I passing by a guy sitting down when he lifts his crutch into the air almost hitting my friend in the head. Like when he saw us and his friend said he almost hit us he goes “idgaf.”

Like we didn’t get hit but the reaction not even being like “oh shit my bad” but “idgaf” is so interesting to me. Like were you trying to look cool to your friends all nonchalant like or cool or something? The combination of carelessness and lack of social awareness is so bizarre.