An emoji is an electronic icon used to express an idea or emotion.
But Judge Kevin Phillips was not versed in the online lexicon.
"What's an emoji?" he asked defence counsel Sarah Saunderson-Warner.
"It's one of the little characters sent after a text," she said.
"Do you do that?"
"Sometimes."
"Was it a smiling one?" the judge said.
"It was an aeroplane," the lawyer replied.
Judge Phillips said it suggested Coake was "coming to get her".
"He accepts it was threatening in nature," Saunderson-Warner said.
Coake came before the Dunedin District Court having admitted a charge of breaching a protection order, which had been made in favour of the mother of his child in 2010.
After attempts to force his way into her new life failed, the defendant planned his next move from Porirua.
On September 15, he sent her the threatening message on Facebook and, despite the victim pleading with him not to come south, he had a ticket booked for the following day.
Coake was jailed for eight months.
Six months of post-release conditions were imposed, barring him from contact with the victim without permission of probation.