Does seeing one's neighbor in the morning make the day ominous?

There is no connection between seeing a person and harm befalling the seer. Believing this is a forbidden form of pessimism, and it is a type of Shirk (associating partners with Allah). If the pessimism involves believing that the object of ill-omen is the true doer of harm and benefit, then it is major Shirk that expels one from the fold of Islam. However, if it involves believing that Allah is the One who harms and benefits, but the object of ill-omen is merely a cause, then it is minor Shirk.