Is it permissible for friends to laugh at or remind one another of funny slips of the tongue if they caused harm, and is a person blameworthy for a defect in themself if they can rectify it or not?

Mocking a Muslim is forbidden by Islamic law. Laughing at a Muslim's slip of the tongue is prohibited, unless it is involuntary, because it involves gloating and mocking the afflicted person. It is not permissible for friends to mention your slip of the tongue to mock you, and if they persist in mocking, then they are not good companions. You should not pay too much attention to what people say, for a wise person strives to rectify their shortcomings as much as possible.