It's probably okay to laugh if you choose to process it as a paratelic (ie funny / playful) thing rather than a real event. All it really says about you is that you find slapstick forms of humour funny, which is a culturally determined thing (where "culture" can be as specific as "culture of a particular group of friends"). You'll almost inevitably find funny what the groups you want to fit into find funny.

The choice (albeit unconsciously and instantly made) to process it as a paratelic thing is a little more ethically problematic. In this case, as Dayve observes, we're told that the guy lived, and we are encouraged to assume (since it's being shared as a joke) that everything's alright. That's probably enough reason to excuse deriving enjoyment by processing it as a funny thing.

You could probably even be excused for processing it as a paratelic thing if you where there when it happened. Depends on the circumstances and on why you're laughing. I imagine that seeing a guy speared in front of you would create a fair bit of tension/anxiety, and laughter is a classic coping mechanism in such circumstances. That'd be an okay reason to give it the paratelic treatment, if only briefly. Laughing when bad things happen can be a really positive way of responding.

On the other hand, if you saw the guy speared, felt no tension and gave it the paratelic treatment purely because you like to laugh - well, it might indicate a disturbing lack of compassion. Treating the whole world as a joke may seem fairly innocuous, but it's an approach to living that shirks the duties that we have as human beings (like compassion).

</ethical analysis>

Poor guy.