I was about 16, my brother 11 or 12.
We were in the living room, I was sitting on the couch. One of the family cats, Simon, was standing on all fours in front of me, his tail in the air. My odd little brother was pointing at the cats butt and laughing, his finger just an inch from his target.
Sensing an opportunity, I threw my arms out and yelled, absolutely startling the cat, who moved straight backwards- my brother's finger slid right up into the cat's rear end all the way.
For a split second, the cat and my brother had the same expression on their faces, absolute shock and surprise- then the cat took off like a rocket, and my brother was yelling, looking at his finger in horror.
I laughed so hard I couldn't breathe. I still thank the Lord for setting it up for me, half a century later. Never gets old.
That cat and my brother could never look each other in the eye after that.