I don't think any stutterers would be offended and if they were I doubt they would say anything to you. Most people stutter to some degree especially if nervous so I don't think it would be immediately obvious that you were imitating someone who stutters. Just do it! Join us in the world of awkward coffee orders :) I think an SLP with experience stuttering would be more valuable to me than one who didn't want to hurt stutterer's feelings. An idea for your assignment though, if you find yourself introducing yourself to a person or group of people you should try stuttering then! I've never had comments on my stutter except when introducing myself.