I think two big factors are the size of your company and your relationship with your boss. If it’s a small company, say 100-300 people, then HR is probably ineffectual and a rubber stamp / protectorate of management. If it is large, especially really large (thousands) then HR is generally responsive and really concerned about such things as discrimination and accommodating disabilities (as a stutter I hate thinking of myself in that way, but I think it certainly fits in part). But consider the second issue before acting. What is the quality of relationship with your boss? Really good, from your perspective (prior to this incident)? What do others think of this person? If they are considered arrogant, asshole etc, then your path is clear. The problem is, if you work in a tight group with little flexibility to work under someone else you got some tough choices. If it was me and I was in a small company and the boss was at least OK, I’d have a sit down with them. Open your heart and let them know how hard it’s been on you and how you fear for your future. Small company and an a-hole boss? Same, but look for another job. Big company good boss? Have a sit down and explain the hurt and fear. A-hole? Go right to HR. Maybe consult a lawyer first to see if stutterers fall under protection. That would be a beautiful lever to use in a big company with an a-hole. I’ve been in similar circumstances twice. Once when I just started a job out of grad school. At dinner with about six of us my boss mocked me at the table. One guy giggled, others silent. I still relive it. I did nothing. I fantasize about turning the table over on him etc etc. this was decades ago! I’ve talked to others I knew at the firm about it. In any case, I left there and got another job within a year. Worked out much better. You have to find a humane place. The second was where my boss was presiding over donut day in the morning with about 20 of us standing around and he mocked the CEO of the firm (a firm of about 20,000) who stuttered. This was a great company. This guy was a known a-hole. I did nothing but transferred offices shortly afterwards, partly to get away from this guy (although I had other reasons to move to San Francisco from Sacramento!)