Mad at his girlfriend of a week Darren Kelvin Millar threw a letterbox through the kitchen window of the house she was living in.
Millar, of Masterton, was convicted of intentional damage and fined by Judge Arthur Tompkins following a defended hearing in Masterton District Court on Tuesday.
The court heard from three witnesses about an argument at the Cameron Cres house on October 8 and the window-smashing incident after midnight on the same day.
He had insisted to police he was at home in bed but the attending officer noticed his trousers were wet at the hem.
Judge Tompkins said Millar's denials were false and police had proved their case against him. The judge fined him $250 and also ordered he pay $103.74 reparation for the broken window and $75 for witness costs.