it means you already own an article of clothing in that category that has a higher amount of mojo.
so, for example, if you have the "Russian Cap", then the "Hard Hat" will have a negative mojo number on it, but anything else that isn't a hat won't be affected by owning the Russian Cap. However buying the item that has negative mojo listed WILL NOT affect your mojo as you will only ever wear the best article of clothing for that category.
