I was going to write a long drawn out post critiquing LB's logic full out sentence by sentence, but then A, I got lazy, and B, I realized that I can sum up the entirety of the problem with three sentences.
1. Words can have multiple meanings that have some overlap, and multiple words can mean the same thing, excepting connotations.
2. Context for a word, phrase, or sentence matters.
3. Conversation is not equivalent to prose.
1: Every single word, every single definition of every single word means something different to everybody. The entire body of one's life changes how they understand various words and how they use them, but despite this fluid meaning overall, at any give usage one has a definite meaning by their word choice.
2: You can't just take something out of context and expect to get the full meaning.
"Fuck you"
alone means little other than distaste to some degree.
"Fuck you, I trusted you"
shows hatred because of some betrayal.
"Hey, long time no see"
"Fuck you, man. I thought you were dead"
It's lightly berating to tell speaker A not to do that again.
Context matters, you can't take that out and then expect full clarity.
3. When people speak aloud, everything is off the cuff and as it comes to mind. It's also usually accompanied by body language as well as other non-verbal information. You can't expect everything that comes out of people's mouths to be a fucking literary masterwork. See that there? That fucking was used as a modifier to place emphasis. It had no other meaning. Yet by LB's expectations as I understand them, it must CLEARLY indicate that the literary masterwork is ACTUALLY having intercourse, which is obviously not true.
So to go back to the conversation that started this whole discussion:
"Hey, bro."
"Buddy!"
"Sup, man?"
"Fuckin' keeping it real, you know?"
"Dude, you're the man!"
"Shit, I know, right?"
"Bro, you know it man!"
"Later, buddy."
"Take it easy bro."
LB's takeaway: Hi, bye.
Applying rule 1: Not much can be gained, but it is understood that to them all of their words mean something as opposed to nothing but hi, bye.
Applying rule 2: The first two lines obviously are greetings, but the third one is inquiring about the other's health. Then B says something extremely colloquial, which urban dictionary helpfully defines as: Staying true to yourself, your faith, your life and constantly seeking the truth. In that, "Fuckin'" serves to emphasize that he is doing what he loves. "You know?" is rhetorical, and is inquiring whether or not A understands him. Then A acknowledges he understood, and that he envies B and compliments A on his enjoyment of life. Then B interjects (IN-TERJECTIONS, FOR EXCITEMENT, AND EMOTION!) with "shit" for the sake of expressing that he like the situation. In that situation, "shit" really has no meaning at all. It's purely an interjection to show obviously positive emotion. Despite me completely understanding the meaning of it, I have no way to express my understanding. It's some combination of joy and appreciation. B was able to convey this combination, which admittedly is probably slightly different for him, with one word, and wait for it... A shows that he understood completely through some combination of that interjection and body language immediately. Then it's just them saying goodbye.
Applying rule 3: This really just explains the horrible sentence phrasing/questionable definitions. They understood what each other mean, and that's really all that matters. They don't care to make their conversation understandable to others.