Is it wrong to laugh at this boy?

im the teacher of a speical needs class and theres this one little retard who just drools and spits all over him self and i just cant help but chuckle i feel bad i know but the parents are the ones one brought up how funny it is, some times we tell him there are snakes in his clothes and he just freaks out peeing and pooping all over the place i cry its so funny , whats wrong with me?