What kind of people are "unfit guys"? Do you call it to someone who is bad? What other expressions or words you use to say it?
Can we call bad friends, "unfit friends"?
"Unfit guys" to me simply means that they do not have a good fitness level. They need to go to the gym or do some other form of exercise in order to "get fit".
If something is "unfit for purpose" it means that it does not have quality/qualities required to fulfil a particular purpose. You don't say that about people or about your friends.
You might say "That guy is horrible. He's rude and vain and has no consideration for others. He's not fit to be my friend".