Funny or Cruel - Where do you draw the line

[Black Lazerus]

Yesterday while playing pool there was a guy ( don't even know who he was) who obviously had to much to drink and was being loud and a general pain in the ass.
so he starts play fight with his boy he pushes him and his boy pushes back his leg buckles and he falls down like a rock. Right next to my feet. His friend tryies to help him up and he pushes him away saying don't touch me
I start laughing even though he is in pain
1. from the look on his face when he went down
2. because he was awfully quiet then
3. I found out later from hearing his friends talk that he had knee surgery and shouldn't have been playing in the first place.

I laughed for a good 20 minutes till tears formed in my eyes. so do you think thats funny or am i just a cruel bastard.

and also i ask have you ever laughed at something that you thought was funny but everyone else thought was sad or just not laughable.