Do you know how much troublesome is try to make a toothbrush stay upright on a plane so that bristles don't touch the surface? I try to do that every morning and I still can't do that! So I usually keep my toothbrush in a cup, but it hardly fit into the bathroom cabinet, and it has to be cleaned very often. If you're accustomed to buy always the same toothbrush you can make this useful holder.
Step 1: The Part List
You don't need too much tools, but maybe you've to steal in secret your girlfriend toothbrush, wait to trash your last one, or to open another brand new one, so to have two of them. Then of course you need a little package of Sugru. I've used white because is one of the last left ones from the eight coloured mini packs.
Step 2: The Kneading
Open your Sugru pack cutting all around, and roll it until it reach a cylindrical shape about one inch wide. Work on a flat surface which you can keep wet and wash after removing it.
Step 3: The Molding
Dampen the two toothbrushes and push them on the cylinder so it wrap the two handles in the narrow segment. the material has to cover the handles for about 10-15% of the width, so to keep them tight. If the handle are wet they shouldn't stick on the Sugru.
Step 4: The Drying
Before the Sugru dries himself off, transfer everything on the vertical surface and push it so it will stick. If it will not stay still due to the toothbrush weight, wrap it with a tape, leaving toothbrushes in place, until everything is dry.
pay attention it will not interfere with the internal shelf, as it almost happened to me ;-)
After some time (I waited some hours) you can remove the two toothbrushes and verify the joints work properly.
Now you've a very handy toothbrush holder, you don't need to become a professional tightrope walker to let the toothbrush remain clean, and you neither have to clean your bathroom cup every day!