We do have to recognise that having a main character complex is not inherently a bad thing. For many of us, our lives may not be the most interesting: we wake up, go to uni, perhaps go to the library, maybe you will go to work, come home, go to sleep, rinse and repeat. The repetition and mundanity of everyday life can honestly make it difficult to even get through the day. Seeing yourself as a main character can sometimes help you romanticise your life and make everyday scenarios more interesting. As well as this, if you find yourself going through a tough time, having a main character complex can help you view this from a different angle.
However, like many things, there are ways you can take this too far. Having such a huge main character complex to the point where you believe everyone else’s lives revolve around you and your life can be inconvenient at least and upsetting at worst. Being obnoxious in public spaces to get reactions from ‘NPCs’ isn’t funny but rather shows your lack of regard for people around you. Dismissing others' concerns or views for your own since you’re the main character can also come across as very rude, and to some people, narcissistic.
Having a main character complex shouldn’t have to come at the expense of other people. Romanticise your life, grow as a person, have fun, but don’t become the main character people end up hating.