Irresponsible means failing to do what you should do or not thinking about the consequences of your actions. When you're irresponsible, you ignore your duties or act carelessly without considering how your choices affect others.

If you promise to water your neighbor's plants while they're away but forget to show up, that's irresponsible. If you leave your bike in the driveway where someone could trip over it, knowing better but not bothering to move it, you're being irresponsible. An irresponsible student might wait until the night before a big project is due to even start working on it, then blame everyone else when it doesn't turn out well.

Being irresponsible isn't the same as making an honest mistake. It means you knew what you should do but didn't bother, or you acted without thinking when you should have known better.

Everyone acts irresponsibly sometimes, but patterns matter. When someone consistently behaves this way, people stop trusting them with important tasks. Teachers won't pick them for meaningful roles. Friends won't count on them. The opposite of irresponsible is responsible: reliable, thoughtful, and trustworthy.