A way to express your reactions to something. For example a loud and long bouh means you are angry. A calm nice bouh means your happy. A normal loud bouh is surprised. etc.
(croud) - SURPRISE (you) BOUH!
(sibling) - I told mom na na nu boo boom (you) BOUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUH!!!!!!!!!!
etc.
In the process of atempting to say the phrase "my bad" but you are too drunk, high, or maybe even both to pronouce "my bad" in the correct manner. Therefor, being intoxicated, the words "mouh bouh" come out of your mouth.