Short of walking around with you fly down all day, is there anything more mortifying than looking at yourself in the bathroom mirror and seeing a whole fucking stalk of basil in your teeth? You immediately start thinking about every conversation you've had since lunch time. Hopefully you had something with basil in it a lunch, or you can get very down on your own personal hygiene habits.
Finding themselves in this situation many people get mad at their coworkers for not pointing out that they look like they are growing a chiapet in choppers, but I totally understand. I don't like being the one that has to tell someone that they are guilty of an appearance faux pas, so I normally just let them find out on their own, like I just did.