#1 Using the Toilet Brush and Putting It Back In Its Holder
The reason why you should never do this again is along the lines of why you should wash your towels despite your body being clean when using them. It’s an honest mistake so we cannot say that it’s the worst cleaning mistake out there. If you put the brush back in its holder, all the germs and leftover water from the toilet will get trapped there.
Not only will the germs end up multiplying, but they will also go right back into the toilet when you use the brush next time! Avoid all this by letting the brush dry completely before you put it back into the holder. It will also save you the slight odor it will pick up when you put it in the holder immediately.
