How kind is it to let someone talk with spinach on their tooth, or a piece of toilet paper hanging off their shoe or caught in their pants?
Yet I have been around people who will let their friends walk around like that without telling them “for fear of embarrassing them” (ohhhhh)
I always point it out. Let the person feel their discomfort. They fix it, thank me and move on.
Probably thinking 
hmmmm…I wonder, I ate that 2 hour ago and talked to so-and-so and so-and-so and …