If I scan someone's ports on a Minecraft server, then make my own bungee cord server, and try to come on with the name of the owner, but I don't get any rights, is it lagal or illegal? So basically, if you want to use the bungee cord gap, but it doesn't work, can he report me for it? Does the "rule" also apply to "your own bungee cord"?
It's not just illegal, it's criminal. Something like that falls under data theft and every operator of a server can report you and possibly ask you to pay, or your parents. If the server is e.g. If it is run commercially and there's a loss of income, everyone will report you.
It doesn't matter whether you do this on your own server or try it on a stranger.