I used to put soap on my brother's toothbrush everytime we got in a fight
Why did you want to put soap there?
I thought that it was a hilarious joke each time that I did it.
That is quite a harmless prank, but you still shouldn't mess around with is belongings. What if he was allergic to eating soap, you would be responsible for all his care and problems from it.
You are just too serious about pranks, relax
I guess I am. I just don't want you to get into trouble with your parents.