Formal situations:
* Yes, capitalize: In a formal setting, like a business letter or a speech, you would capitalize "Good Morning" and "Gentlemen." This is because they are treated as proper nouns, acknowledging a specific time of day and a group of people being addressed.
Informal situations:
* No, don't capitalize: In informal situations, such as a casual conversation or an email to friends, you can lowercase "good morning" and "gentlemen."
Other considerations:
* If "Good Morning" is part of a title: If "Good Morning" is part of a title, like "Good Morning Gentlemen: A Guide to Etiquette," then it should be capitalized.
* Consistency: Maintain consistency within your writing. If you choose to capitalize in one instance, stick to it throughout.
Ultimately, the decision comes down to the level of formality you are aiming for.