What do we mean when we say it today?
Nowadays, people are usually quoting Shakespeare when they say "friends, Romans, countrymen, lend me your ears." It could be a conversation starter for people to be quiet, or just a joke that gets people to listen to you.
If you do use this phrase, you're in good company.
Outkast, The Cosby Show, The Beatles, The West Wing, and even Sponge Bob have used some part of it before. We'd like to point out how varied that list is. That's how classic this phrase is. In fact, some scholars think "friends, Romans, countrymen" is the most quoted line in Shakespeare (after Hamlet's whole "to be or not to be" thing, of course).