The "bovine" joke in The Restaurant at the end of the Universe by Douglas Adams (The Hitchhiker's Guide to the Galaxy series).
The whole “bovine” joke was hilarious on one hand and a little horrifying on the other. It got me thinking: how would I feel if an animal I was about to consume came up to me enthusiastically conveying its consent for being eaten? I will be horrified, just like Arthur! But why?...