I don't know. I mean, how un-human can you get? Films are there for entertainment, i.e. to make you laugh or cry or have a good time. Cackling is really one of the most subdued expressions of laughter. With a background noise that is likely around 90db it shouldn't bother you. If it still bothers you I'd ask myself some serious questions as in: Am I jealous that someone else is having a good time? If so, why?

Now if the person is laughing aloud slapping his thighs every two minutes, that's different, or if he is indeed poking your sides. This could be construed as a nuisance.

But frankly, to say cackling passengers are the least favorite is quite far out. What about violent, obscene, stinking, fat, sick, impolite, ceaselessly talking people or screaming or kicking kids?

If the cackling passenger is the biggest problem, then there is a bigger problem behind it.

Till