Would I be wrong for turning my little brothers xbox off in the middle of a fortnite game.
Why do you want to interrupt your brother's game?
He's complete trash when it comes to honesty
I get being mad at your brother if he's been lying, but interrupting his game is not a good way to solve your problem. He will just get angry. Wait until he's not playing the game and try to talk to him about the importance of being honest.
I'm doing it right now because I am sick of his behavior and I'm going to prove a point.
Causing conflict and tension between yourself and your brother is wrong. As an older brother you should be setting a positive example. Turning off his game will only show him that it's okay to be disrespectful.