I taught my friend's little brother to eat sand.
Why would you teach his little brother to eat sand?
Because he told me I don't have any friends.
I understand that it's not fun to be made fun of, but you shouldn't take it out on children and make them eat dangerous things. Children are very impressionable and it is horrible to take advantage of that, you may hurt them even more in the future.
My friends little bro is old enough to know better.
You may think he is, but it's still not right to get him to eat sand. You don't know what kind of damage that could cause. I think it would be better if you just ignored your friend's brother, instead of trying to get revenge on him.