As everyone has said, that's an outrageously shitty thing for them to say to you. I'm not sure if it's just me, but I know when something is stressing me out, I stutter more. If I'm comfortable and relaxed I tend to stutter less. I know it's hard, but just forget about it. Fuck em. It might seem like it now, but you don't need their shit. Just focus on you and relax. When I can focus on what I'm saying, I can normally avoid the words that cause me to stutter (w, u, & l). Fake it until you make it.