Your mouth or balloon blowing are very bad examples, the reason is because there is no obvious reference.
A McDonalds straw is a better example. Say that it's 7 inches long. You know the density, you know gravity.
$$P=\rho g h$$
In this case, the full 7 inches will get you about 17 mbar. From my everyday experience and intuition, I believe that I can maintain a pressure in my mouth or blowing up a balloon several times what is required to suck up a (watery) drink the full length of a straw.
100 mbar is likely to overwhelm your mouth, but it might just be "athletic". In order to test it, you'll only need a few pipes from an aquarium store, a tub, and maybe some clamps (unless you have more specific equipment). Looking at some anecdotal information online, I see some people reporting in the neighborhood of 2 psi (137 mbar), corresponding with reports that "it felt like my eyes were about to pop out of my head".
Remember, safety first!