Constructive criticism is often very much appreciated, give. Give feedback based on the presentation of work and make the person understand that what you are addressing is their style of delivery and not the person directly or their personality.
You often get people thatwho say certain things like, after"After you pointed out my robotic/monotonous voice, iI have significantly improved my mode of teaching." Try to give honest feedback at all times but use words wisely to differentiate between the person and their delivery of work.