"Our intention is never to make fun of anybody who has allergies, but to make sure we highlight the fact that having an allergy is a serious issue," said the post.
It had generated more than 60 comments by 6.30 last night.
Dion McCracken, whose son has a serious nut allergy, was not convinced by the explanation.
"Great for Adam. A shame for my son who may now be exposed to kids at school thinking your prank was a great idea," he said.
"If one kid that watched the prank thinks it's funny to smear peanut butter on an allergy kid, there is a very real threat of anaphylaxis and rapid death.
"What Now didn't have ill intent, but they've just taught thousands of Kiwi kids that doing this isn't a big deal. It really is."
Claire Eveleigh said she was going to lay a complaint.
"It's very scary that you are defending yourself on a topic you clearly do not know much about. Not knowing is OK ... but broadcasting on TV about it is not OK ... I will be making a complaint to the BSA about this."
Whitebait-TV, which produces What Now, was unable to be reached for comment last night.
A spokeswoman for TVNZ said if people were offended by the show they could make complaints through the BSA.
Peanut allergies
* 1 in 50 infants are allergic to peanuts.
* It's the most common food allergy.
* Exposure is hard to avoid and in some cases even trace amounts can trigger symptoms.
* Symptoms include: Hives, eczema and vomiting and in serious cases anaphylaxis - breathing difficulties.
* Treatments include: Adrenalin injections are required as soon as possible after exposure but it also recommended that asthma-sufferers keep that condition well controlled to avoid extra complications.
