The 41-year-old game show host stumbled upon the phallic work of a ballsy graffiti artist - and took his Instagram followers along for the big clean-up.
In the video shared to his Instagram page, Grant can be seen standing in a bus shelter, scrubbing his Celebrity Name Game poster with a cloth.
Followers could see quite clearly that Grant's forehead was decorated with penis.
"It’s not coming off. All I’ve done is made it the cleanest dick in Sydney," he joked.
A school boy then appeared as he waited for a bus.
"Hey, bro," Grant said. "Was that you? Did you draw that picture?"
The boy said no, and said he had no idea who the guy on the poster was when the father-of-two quizzed him.
The cheeky Gold Logie-winner then captioned the play-by-play, "Weirdly, if I rub it any harder it gets bigger. 'Dear Vandal, I have a very particular set of skills. I will look for you, I will find you and I will kill you,' Grant Neeson," he joked.