If you are not a parent but you hate someone and want to make life miserable when they have kids here is your Christmas list.
Legos- Whoever came up with these hates humanity. I am fairly certain they are also self-aware based on the fact that they always find their way into the hallways of my house and somehow under my feet in the middle of the night even though I know I swept the hallway for obstacles and traps before I went to bed. These jagged little monsters could only be made worse if they made them out of rusted metal.
Repetitive noise toys- The louder the better. Have you seen the scene in The Walking Dead where they had Daryl locked in the closet playing the same music over and over until he broke? Same thing here. Children have the ability to torture you with the same song for months on end without even phasing them.
Board games for young children from your childhood- Nothing ruins your day quite like deciding to set down with the family and try to teach the kids a board game that you loved as a child only to have half the pieces missing and then you manage to step on any of them that are sharp later in the night.