selfishly
In a way that only cares about yourself, not others.
Selfishly means doing something in a way that only considers your own wants and needs while ignoring how it affects others. When you act selfishly, you're thinking about yourself first, second, and third.
If you grab the last slice of pizza without asking if anyone else wants it, that's acting selfishly. If you hog the playground swing for an hour while other kids wait, you're behaving selfishly. If you pick a movie only you want to watch without caring what your siblings prefer, you're making a selfish choice.
The word describes the manner or spirit in which someone does something. You might selfishly refuse to share your art supplies with a classmate who forgot theirs, or selfishly monopolize the conversation at dinner by not letting others talk about their day.
Acting selfishly is different from simply taking care of yourself or having preferences. There's nothing wrong with enjoying your own slice of pizza or having a turn on the swing. The selfishly part comes when you take more than your fair share or ignore how your actions affect the people around you. When you notice yourself acting selfishly, it's usually a signal to pause and consider whether you're being fair to others.