Origin: This phrase might have been derived as an allusion to the loose connection between “baby” and “bunny.” The phrase originated in the 20th century. The first citation you can find is in Nicholas Monsarrat's Cruel Sea, 1951: “’I bet you left a bun in the oven, both of you,' said Bennett thickly... Lockhart explained ... the reference to pregnancy." 🏡 @English_House 🏡