1) A person that smacks cocks. 2) A term used to comment on male's mastabatory habit. 3) An insult one uses against people that cause harm or discomfort.
Several meanings. Most commonly refered to as one who is doing stupid things, as in a person who is so out of it, they are trying to smack crack into their skin directly. Also, can be used as a term of endearment, or torment depending on the person.
don't taunt the bullwith thatred cape, you crack smacker.
or,
that was so sweet of you to buy me those flowers you are such a crack smacker