According to martin & nakayama, chapter 3, jeff accidentally insulted the parents of his roommate mohammed by putting his feet up on the desk when they were visiting their dorm room. jeff's behavior (and subsequent apology) illustrates that communication can be

unintentional

Explanation:

Unintentional communication refers to the situations when the person do something which is also interpreted by the another person but the first person don't knowingly mean to do that thing. It is always non-verbal and it is demonstrated unconsciously.

Jeff insulted accidentally Mohammed's parents illustrates unintentional communication.