As with most of the great conversations, this was started at the pub. I was out on Boxing Night with old friends Raz and Yvonne, though it was the first time they had met each other. The chat moved onto pulling and it quickly became apparent that Yvonne was unaware for the phrase "Cockblocking" from the verb: to Cockblock………..
Cockblocking, we explained to Yvonne, is a phenomenon can occur when a man is talking (or other form of social interaction such as dancing) with a member if the opposite sex (or the same sex if you are so inclined) and the interaction seems to be progressing to a more romantic level, i.e. the game is on. Cockblocking is essentially when a friend or other human stops you pulling a particular girl. The female equivalent also exists and is known as "Titblocking". The conversation was recorded for posterity and the vital points have been transcribed for future generations.
Cockblocking can happen in a number of different ways that can, if not dealt with properly, result in the worst case scenario – you don’t get the girl. By its nature cockblocking can be competitive, passive, malicious, accidental, indirect or a combination of the above. These are expalined below.
Competitive cockblocking: You don’t get the girl because another person interferes with the situation by trying to pull the same girl. The cockblocker should always be a person that is outside your circle of friends; however, it is not uncommon to have a mate that is known to cockblock in such a fashion. Any friend that cockblocks in a competitive manner does so as a direct infringement of the "Law of the Wingman" and the "I saw her first" treaty. The cockblocker may or may not be aware of your progress with a particular lady (see malicious and accidental cockblocking). 
Passive cockblocking: This is essentially the opposite of competitive cockblocking where the cockblocker has no intention of pulling the same girl but directly interferes with the situation and so stops you from pulling. Again the cockblocker may or may not be aware or the situation or your progress with the targeted individual. Despite the seemingly benign term, the threat of Passive cockblocking is actually greater than that of competitive and should be taken seriously. The passive cockblocker may potentially be anyone of a myriad of people, whereas the numbers of suitable competitive cockblockers may actually be small in any given place. The passive cockblocker may be anyone of the following people:
1)      One of your attached or married friends or family who can’t read the situation.
2)      One of her attached or married friends or family who can’t read the situation.
3)      A drunken friend of yours or hers who cant read the situation.
4)      A friend of hers that is disgruntled at being left on her own.
5)      Random idiots that can ruin the moment by , tripping, spillage of drinks, vomiting etc on either of you or very close to you both.
6)      A friend of yours that “thinks it’s funny” to cockblock you with no intention of pulling her (comedic).
7)      A friend of hers that is trying to pull you, i.e. competitive titblocking her friend (rare).
8)      A female friend of yours can’t read the situation. They can often be perceived as a threat.
The use of a wingman is especially important for mitigating the occurrences of 3) and 4) by running interference with her friends simply by talking to them or “taking a hit for the team”.
Malicious cockblocking: This is when the cockblocker is fully aware of the situation afoot and chooses to disrupt your chances of scoring. This may be either competitive or passive. Neither of which is acceptable. In some cases a passive malicious cockblock may also be “comedic”. This is a situation when a friend or friends of yours disrupt your progress because they “think it’s funny”. The truth is – as long as you’re not the victim (or target or mark) of the comedic cockblock – it’s hilarious. The hilarity can actually be heightened by taking turns or tag-teaming the cockblock. Be warned however, this can only be tolerated for short periods of time before the victim explodes in fits of rage!
Accidental cockblocking: Occurs when the cockblocker is unaware of the situation but none the less manages to get in the way. This can usually be rectified by subtly informing said person of your concerns, at which point apologies can be made and off they trot. If the cockblocker chooses to stick around in spite of the new information this can now deemed to be malicious and should be treated as such.
Indirect cockblocking: These are essentially all the other human based situations that may occur causing you to fail in the pursuit of pulling! You should be fully aware of these as they do pose a real threat! The cockblocking usually occurs because one or more of your mates quickly detreiorate to a level that means that they cannot take care of themselves forcing you to become their carer thus forfeiting any potential lady joy. These include but are not limited to the following situations:
1)      Someone you are with becomes excessively drunk.
2)      Someone you are with starts crying uncontrollably (usually female). 
3)      Someone you are with gets involved in a fight (usually male).
4)      Someone you are with doesn’t get on with the rest of your friends, forcing you to spend more time with them.
If you are the victim of a cockblocking episode it is more than possible to ride it out. The most important points take away from this are recognise to be aware of cockblocking hazards and to know are that prevention is better than a cure. This means that if you know you have a friend who is prone to getting drunk and passing out, palm them off onto another mate. If you have a friend that is prone to the odd competitive cockblock make sure to let him know that you aint gonna stand for it this time!