Drunken Michael Palmer broke into his mother's home and assaulted his sister's boyfriend.
Palmer headbutted the man, breaking his nose.
At St Albans Crown Court yesterday, Palmer, 21, of Pickford Hill, Harpenden, admitted a charge of assault occasioning actual bodily harm.
He also pleaded guilty to damaging property at his former home in Artisan Crescent, St Albans.
Kevin West prosecuting said it was the early hours of June 1 when the defendant went to his mum's house.
She was away at the time and the court was told that, because of a fall out, he was no longer living there.
But in the house at the time was his sister and her boyfriend.
Palmer, who had been drinking, started shouting at his sister and when boyfriend Jonathan Waller asked him to calm down, Palmer headbutted him, breaking his nose.
He fled the house but was arrested a short while later.
Mr West said Palmer had caused £200 worth of damage at the house.
The court was told Palmer's own girlfriend is expecting their first child in February.
Passing sentence Judge John Plumstead told him "You were out of control and raving drunk."
He sentenced him to nine months imprisonment but suspended it for 18 months.
Palmer was also ordered to pay Mr Waller £500 compensation.