The interviewer who laughed is human trash and I'm so sorry that happened to you. If you don't get the job I would maybe call them out on social platforms or leave their company a bad review. I wouldn't let them get away with it. On a more positive note I'm a 43 year old female and I've stuttered my whole life. I stutter worse during interviews, as I'm sure we all do, but I've never really had a problem getting jobs, my current job I could barely speak during the interview but still got the job (as a store assistant in a charity shop which often involves serving and speaking to customers). Thankfully employers and people in general are more aware of stuttering these days and not being dicks about it. Unfortunately you got a dick interviewer this time.