There are people who don't understand the concept of "companionable silence". There are people who feel that any gap or pause in conversation is void that must be filled. Sometimes you can ask 'em to pipe down, but that doesn't always work, and it can be perceived as rude anyway (not that we mind being rude if the situation demands it) This is why you need a stop talking shirt.
Someone bumping their gums incessantly, yammering away even though you're clearly not interested? Point to the front of your shirt.
Someone chipping their teeth about something they don't know shit about, or about a topic you could care less about? Point to the front of your shirt.
Is someone trying to engage you in conversation while you're reading a book, watching a movie, or (God forbid) before you've had coffee? POINT TO YOUR SHIRT.