My dad and I have always had a good ongoing joke about his "moobs." They're not particularly large, nor is he, but it's just something we've always joked about. Whenever he would walk past me while I was on my PC, I'd reach my arm out and go "HONK HONK!" as a prank. He'd try to be angry, but every time he'd get a good laugh out of it instead.

Because my room is the dining room, which you have to walk through to get to the back garden, he would walk through quite often. One day, it was pouring rain. I hadn't seen my dad yet that day, so I assumed he was working on something in the shed. Then I saw him walking from the back of the garden towards the door.

He had his black raincoat on with the hood up, and he came in. Me being pre-occupied by my game, I did not look at his pants or shoes. I proceeded to extend my arm, grab his chest, and yell out our usual joke catchphrase.

It wasn't him. It was my sister. We didn't talk for a while after that, and it was incredibly awkward. I eventually explained the situation to her—that I prank Dad like that all the time, and because she was wearing his coat, I assumed it was him. She just said, "Oh.. okay," and that was the end of it. Safe to say, I retired that prank for good!