Don't ever feel bad because you're struggling with a disability. And don't use the r slur. Not towards anyone, but certainly not towards yourself. If someone is disrespecting you during a presentation, do not hesitate to bring attention to their BS. Feel free to walk right behind them and continue your presentation over the tops of their heads. Or ask them to leave the class. When you are presenting, that room belongs to you. It takes great courage for anybody with a stutter to stand up and talk in front of people. Anybody who cannot respect that effort can GTFO.