"Good morning. To whomever has been enjoying my coffee creamer all week ... Surprise!!!
"You've been drinking my breast milk. Hope you've enjoyed - cheers!"
In case her horrified thief was concerned for their health, thoughtful "B" noted drinking breast milk is harmless: "Ps. It's organic. So no worries".
The photo has been liked more than 12,000 times on Reddit with some users suggesting the theif should be grateful for the added nutrition they would have ingested from the breast milk.
One user wrote: "I would find out who it was and charge them for the great nutritional supplement they got for free.
"Bet they felt great that week and didn't know why!"