Uenuku Thompson threatened family members with a kitchen knife after being told that his younger sister's boyfriend - who he did not like - was on his way over, the Whanganui District Court was told on Tuesday.
Thompson became belligerent at the news and began to threaten his family.
"I'll stab her if he comes over here," Thompson reportedly said.
He rushed into the kitchen and picked up a knife and began brandishing it around.
"You think I'm crazy, I'll show you crazy."
No one was seriously hurt and Thompson was charged with possessing an offensive weapon.
"I just got upset because my sister's boyfriend was coming over and I don't like him," Thompson told police.
Thompson's lawyer Jamie Waugh said that his client knew what he did was wrong and that Thompson was currently abstaining from drugs which he would like assistance with.
Judge Philip Crayton sentenced Thompson to six months' supervision with a focus on alcohol, drugs and anger management.
"The charge that you faced is not as serious as it could have been," he said.
He ordered that the knife be destroyed.