For me, when I see 'lol' used like this I read it as quite aggressive and offensive. I don't see it really an expression of surprise or shock, but with its original meaning used in a sarcastic way: 'I am laughing with incredulity at the fact that you actually think that'.
lol doesnt mean just laughed...
It also means being shocked or surprised "lol?"
For some reason people who try to define lol often miss that 2nd, popular meaning