However, here are some options depending on the context:
Formal:
* Sir: This is the most common formal equivalent, used in similar situations to "madam."
* Mr. [Last Name]: Using the title "Mr." followed by the last name is also formal and appropriate.
Informal:
* Sir: Can be used informally, but might sound slightly stiff.
* Mister: A more informal option than "sir" and can feel more friendly.
* Sir/Mister [First Name]: Using the first name can be more familiar and friendly, but be sure the context is appropriate.
Other Considerations:
* Profession-specific titles: In some professions, like "Doctor" or "Professor," the title is gender-neutral. You can simply use the title followed by the last name.
* Context: The best choice often depends on the situation.
It's always a good idea to consider the specific context and the relationship you have with the person you're addressing to choose the most appropriate form of address.