Can anybody explain to me what ‘That`s classic’ really mean?
For example, when somebody tells a joke and somesody says…‘ha ha, that`s classic!’
I always assume that it means classic, literally and that the joke has been around for some time. But I also get the vibe of authenticity. Which is it?
A classic joke could be a typical one, though the expression ‘that’s classic’ in the context you gave rather means ‘very funny’:
classic
2 INFORMAL extremely or unusually funny, bad or annoying:
Then she fell over backwards into the flowerbed - it was absolutely classic!
That was classic! That van-driver signalled right, and then turned left.
See also classic (TYPICAL).
(Cambridge Advanced Learner’s Dictionary)
oh thanks Conchita.you`re very helpful 
so i guess when people say
thats classic of him it also means thats typical of him
Hi NinaZara,
Just to add to what Conchita has already said - ‘classic’ on its own often means: That’s typical. That’s perfect. That’s just what you would expect.
Let me give you an example. You know someone who has a very bad sense of direction and always gets lost. Let’s say this person arrives late, apologises for being late and explains they took the wrong turning. Your comment could be: Classic! And that’s how it is used just as one word.
Alan
Thank you Alan.
I think I really get it now.
so, is it really sounds sarcasm or compliment? or both?
It could be either. It’s usually complimentary, but it depends on how it is said.