Really don’t know if you can deaden yourself to not feel when people laugh at you for a condition you can’t really control. It sounds like you can mask your speech? I’ve never heard of someone saying they plan on practicing their stutter more. Lol. I would try to get more of a sense of humor about it versus trying to stutter more to get people more used to it. When your coworker ask you to throw up first. I would say… man I’m trying but it’s not coming up and then just laugh about it. No biggie unless you notice it becoming repeated harassment. Than document everything and go to HR.