There's no need to be embarrassed, forgetting to brush your teeth happens to the best of us on occasion. Perhaps you were in a rush because you were trying to catch your bus or were running late for work. Given that you've gone through your morning routine so many times, it's completely possible to forget to do something and not realize it until you've already left.
Although it's recommended to brush them at least twice a day, forgetting to brush your teeth once won't be the complete end of the world. But you should still do what you can to remedy the problem, whether it be from dental health concerns or anticipating embarrassing interactions throughout the day. Luckily for you, there are some ways to hopefully resolve before anyone can notice.
If you're the kind of person that anticipates as much as possible, you may already be prepared for a situation like this. If you're lucky, you've already got toothpaste somewhere nearby, either at your desk or in a bag. If all you're missing is a toothbrush, you're in relatively good shape. All you'll need to do next is get some water and a paper towel, which can both be conveniently found in a bathroom. You'll wrap the damp paper towel around your finger, place a small amount of toothpaste on it and brush thoroughly as you would with a tooth brush. Make sure that you rinse well and repeat the process if need be.
This is where things get interesting. You may find that you're without any dental supplies at all. If this is the case, you'll have to improvise. Here's a list of nonconventional methods of cleaning your teeth:
Keep in mind that you shouldn't have extended periods of time without using a toothbrush and toothpaste. These methods aren't meant to be long-term solutions as much as they're quick fixes to a temporary problem.