You cannot be charged with a drink driving offence under New Zealand law while riding a bicycle, unless it has a motor. Excess Breath/Blood Alcohol (‘EBA’) charges only apply if you drive or attempt to drive a motor vehicle, meaning a vehicle drawn or propelled by mechanical power under sections 2, 11 & 12 of the Land Transfer Act 1998 (‘LTA’). A bicycle without a motor is not considered a motor vehicle nor is a bicycle with an electric motor of less than 300 watts.
However, this is not without risk. While EBA charges can only apply while driving motor vehicles, some other charges, such as careless driving, are not restricted to your activities with vehicles that have motors. Someone cycling home under the influence could be charged with careless driving if it can be shown they have used their bicycle carelessly or without reasonable consideration for other persons under section 2 & 8 of the LTA.