I laughed at a grieving person this morning
What kind of laugh was it?
It was a cruel laugh.
You shouldn't laugh at someone grieving.  They're probably feeling horrible right now and the laughter sure doesn't help.
I have no sympathy for people who are grieving.
You might feel that way right now, but I bet if you lose someone important to you you'll learn sympathy real quick.  People will be there for you in times like that if you're there for them when they're grieving.