Would you want to try it? Disgusting but something unique to prank someone at night. Just imagine when they is sleeping and woke up from the door knocking. Walking halfway asleep to open a door and feel why the door knob feel so weird normally it is round than like a banana.
Better to prank someone that you hate than someone close to you because you can destroy their relationship. The best thing would be take a video when the person notice and open the door and look at their face it is surely will be epic. It is the best to put some sperm on his/her hand too! Haha