When one interrupts a 2 person comment chain on a Facebook status update, picture, etc. Typically, the original commenters will start a nice, engaging conversation, and then the "blocker" will barge in with a totally unrelated comment, thus disturbing the flow, and consequently delaying your chances of scoring with the hot chick that's totally interested in what you're doing for the weekend...

When someone intervenes while you are in the process of getting something. Often used in cases when one stops you from getting a phone number, information, or something else, from a girl (or guy).
Can also be shortened to "Blockin".

also see cock blockin/ cock blocking

When a person is preventing you from getting you swag or gucci on. This can be considered a cock block.

Similar to cop blocking, only more specific. An interference, that brings a hault to any sexual act involving a man's (or a woman's in some cases) penis. It is sometimes used even when a man (or a woman with a penis) is just talking to someone, this is a stretch but is appropriate as long as their intentions are to eventually have sex with the person they are talking to, and they have some chance. If the person they are talking to shows no interest, and one interrupts...then they are probably doing this person a favor. Either that or just adding insult to injury.

Cockblocking is the action of denieing one of using there cock in a sexual fasion. It originates from the hood although it is not clear which one.

n. one who interrupts an act of sexual intimacy, such as hooking up or having sex, by opening doors, calling phones, etc.

Can also be used in the verb form, "cock blocking"

Cock Blocking Degree: The word is used to refer to anyone whether male or female who either intentionally or accidently interferes with a male trying to meet or hook up with a woman or man. (Usually the interference leads to rejection)

Also:
Slang used to describe someone who repeatedly blocks your balls in pool/billiards (also known as Jap Pool)