inconsiderate
Not thinking about how your actions affect other people.
To be inconsiderate means to act without thinking about how your actions might affect other people's feelings or needs. An inconsiderate person might talk loudly during a movie, not noticing that they're ruining the experience for everyone around them. They might leave their backpack in the middle of the hallway where people trip over it, or interrupt someone's story because they're too focused on what they want to say next.
Being inconsiderate doesn't necessarily mean being mean on purpose. Often, inconsiderate behavior comes from simply not paying attention to others. The kid who slams the door at 6 AM probably isn't trying to wake everyone up; they just aren't thinking about their sleeping family members. Someone who takes the last cookie without asking might just be focused on their own hunger rather than considering that others might want it too.
The opposite of inconsiderate is thoughtful or considerate. When you hold the door for someone carrying heavy bags, wait your turn to speak, or remember to thank someone who helped you, you're showing consideration. You're thinking beyond yourself and noticing how your actions affect the people around you. That awareness makes all the difference between being someone others enjoy being around and someone they'd rather avoid.