Saff, 127 Hours is a movie about someone who goes climibing alone and ends up trapped under a boulder. He has to cut off the lower part of his right arm to free himself – hence the “cut off my right arm” bit. Knowing the story won’t make it any funnier.
Erm, aside from the last comment being obviously intentional, I think they were all trying to lure someone else into falling for the trick. The more people that posted, the more believable it would be to a gullible person.