When your bro plays wingman for you without you knowing. He then, after the fact, tells you about how he hooked you up. Your bro is now entitled to one cock-block anytime and anyplace.
Your bro has a facebook conversation with the chick he's trying to get with as well as her sister whom you had a great time with over the weekend. When you come up in the conversation, he defends you and puts in a good word. The next day in the gym he shows you the conversation and says you owe him for playing wingman. This is legit; he is now entitled to one cock-block which is considered Bro tax.