Mumblemouth

a)A word used to describe someone who mumbles; Someone who you have no idea what they are saying because they are either far too quiet, or they are mumbling (could be a combination of both)

That girl is a mumblemouth, no one can understand her.

Professor Mumblemouth

A knowledgeable grey haired professor, who has a habit of literally mumbling while delivering a lecture, making it hard to comprehend.

Derivation- Inspired by the definition of the word mumblemouth on urban dictionary.

Professor Pandey warned his colleagues- " Speak loud and clear! Or else students will call you Professor Mumblemouth. "