I have a friend whose dad ran a ski resort. One year he used a snow machine to make a bunch of snow, and covered the hill behind the room she shared with her sister. Then he came in and told them it snowed, and to dress warmly for the day. When they looked out the window, they saw snow and believed him. When they went to leave the house, it was 80' and sunny. Hee hee.
The worst one I was a victim of was in high school, when my dad set all the clocks forward to 1:00. Then he came into our room acting all angry, saying that the school called because none of us went. We thought he was pranking us, and he turned on the TV where the news showed 1:00. We all start freaking out and getting ready, when he started laughing. He had recorded the news from the day before. Lol. Then he took us out for breakfast before school, which was really rare as he was usually gone to work by the time we got up for school. :)