A fun thing to do to your parents is to change stuff in their home (even if it's still your home) and see how long it takes them to notice. This is great for people who enjoy annoying people, but when those people are your parents, they still have to love you.
On Wednesday, a Redditor posted a shout out to his brother, who replaced a framed picture of Jesus with a picture of Ewan McGregor as Star Wars' Obi Wan Kenobi. Apparently it's been three months and their parents still have not noticed. Nice! (*high five*)