How to remove quirk? I've already tried the potion

Hmm, perhaps repairing the game might help? I'm not sure as I haven't used the potion myself, but I have removed/added quirks without any issues with testingcheats on, shift+clicking on the sim and choosing "public image". I'm not sure if it matters, but I also did a celebrity cleanse first and then added my sim's celebrity status back with the same cheat (since I had started a new save and wanted a new celebrity tile).