Haha, that's funny
You say 'haha, that's funny' to show how unfunny a joke is, like it was the worst joke ever and you're not even trying to be nice.
'Haha, that's funny' after my friend told me a joke about a ghost who couldn't find his ghost clothes.
'Haha, that's funny' when my friend told me a joke that was just 'I like dogs' and that was it.
'Haha, that's funny' when my friend told me a joke that was longer than a whole movie.