I used to get brother and boyfriend mixed up. Not their meanings, obviously, but just in speech. Mushroom and marshmallow as well, which was interesting when I was a barista asking customers if they wanted mushrooms on their hot chocolate
For me it was personnel and personal till I start working at personnel department of my organization LOL. Then it shifted to effect and affect like it said above. But i am in the process to make it a habit to differentiate between them.