Person who mocks others for mistakes instead of helping?

Imagine a person who warns you not to walk in a particular direction as there is a pit/hole, but you continued anyway and fell into that hole. The person then comes to you and instead of helping you in that dire situation, mocks you for not following his advice.

Is there any specific word (noun) to address such type of people, e.g. narcissist, egoist?

Solution 1:

While it is somewhat broader, the term gloater may apply

to observe or think about something with triumphant and often malicious satisfaction, gratification, or delight: gloat over an enemy's misfortune [Merriam-Webster]

If you will accept a phrase and want to be a bit literary, you could call the person a smug Cassandra

(as noun a Cassandra) A prophet of disaster, especially one who is disregarded. [Oxford Dictionaries Online]

(smug) excessively self-satisfied or complacent [Collins]