Here's a breakdown:
* Modicum: A small quantity or amount.
* Decorum: The proper or acceptable way to behave or conduct oneself in a particular situation.
Essentially, it implies that while someone might not be perfectly well-behaved, they at least make an effort to be polite and respectful in a way that is considered appropriate for the situation.
Example:
"He managed to maintain a modicum of decorum at the formal dinner, despite his usual boisterous demeanor."
This means that even though he is typically loud and energetic, he made an effort to behave in a more subdued and respectable manner at the formal dinner.