During her childhood, my younger sister Janice detested any spices–even salt and pepper!–put on her food. When she was about 11, we were eating spaghetti at dinner and she left the room briefly. While she was gone I sprinkled a little pepper on her spaghetti. She came back and finished the meal. I asked her how she liked the spaghetti. She said it was OK. Then I told her I’d put pepper on it while she was out of the room. Did she ever get mad!! 
My older brother Gary has always liked boiled eggs. When he was on furlough from the Service in the mid-70s and visited, I had bought some things at a local novelty store. There had been one boiled egg left in the refrigerator one night; I ate it and made a substitution. The next morning he went to the refrigerator to get a boiled egg, and hammered the egg on the counter trying to crack the shell. I got a kick out of telling him the “egg” was made of plaster–and hard as a rock!
Please post here incidents in which you played a hilarious trick on a brother, a sister, or another close relative. 
My older sister used to babysit me. (I was about 7) When I wasn’t good she told me she’d kill herself. Then she’d start counting.
When she got to 0 she would stop breathing.
Evil bitch.
–John