This substance already exists: biter nail polish. Apply it on your fingers, and you'll want to avoid touching your mouth at any cost. On a side note, so many

This substance already exists: biter nail polish. Apply it on your fingers, and you'll want to avoid touching your mouth at any cost. On a side note, so many buildings still put doors at the entrance of toilets forcing you to touch the door right after cleaning your hands (or to use a napkin to touch the handle).