There aren't laws for a stutter specifically but there are laws against discrimination and bullying in most countries, should be every country in this day and age but regardless. I don't think the judge meant it in a bad way, we've all laughed at something that's happened that's unexpected, may it be someone falls, their voice cracks, someone as lower voice than expected, etc. Its a natural reaction. What wouldn't be right and would be bullying/discrimination is if the judge began to laugh hysterically over something that would get a mild chuckle at most. I do agree with the rest of your statement!