You're going to have to develop some tough skin and tell folks "Yeah, I have a stutter". You don't have to be a jerk or anything, but accept that you have it. If you don't want to go down that route, than you can just laugh it off. Sadly, even in this day and age, stutter is a disability that people find it okay to make fun of. I've gone through it for years so I kinda grew immune to it.