The vandal failed to make the word "kura" unreadable on the school sign, but it will still cost the council $200 to repair or replace.
A council spokesman said it was disappointing people felt they could vandalise public property, which ended up costing ratepayers.
It made the disappointment a bit clearer in a Facebook post.
"This vandalism seems to have deliberately targeted the te reo Māori part of the sign indicating that someone out there really needs to get over themselves and stop making their little tanty everyone else's problem."
It was posted alongside an emoji of a baby, infantilising the act.
"It costs money to get a replacement sign, and for our contractor to install it. That's time and money that could be used elsewhere on your roading network", the post said.
"These signs are designed to keep kids safer around schools, and I'm sure nobody has a problem with that."
The spokesman said there were about 40 cases of sign vandalism in the last year, including stolen signs, chopped down posts or vehicle collisions.
Among those was a similar case in February, with the word "kura" blacked out on a street sign in Reed St.
"We encourage the public to report vandalism to council, especially when it comes to road signs which have safety as a core feature of their design."
