De Leeuw was introducing a band of women who founded a charity that facilitates milk exchanges between mothers who have too much and those who have too little, when he suddenly inquired of his guests if he can have a taste.
"How does it taste, nice and sweet?" de Leeuw asked.
One of the women who brought a bottle of her milk offered some to de Leeuw, who declined, asking instead who among them would be willing to let him drink from the source.
"Well, if you don't bite you may try it," said a volunteer.
Proving he wasn't joking, the comedian then approached the woman, and proceeded to place his mouth on her nipple.
After a few long sips, de Leeuw retracted his face — only to lunge at the second breast.
"I find the second one better tasting, but I can taste that you've eaten asparagus yesterday," de Leeuw said after his taste test. "Well, not yesterday but Tuesday," the woman responded.
Defending her decision to allow de Leeuw to get up close and personal, the participant, Wendy, told her Twitter critics that "it was for a good cause."