How we change what others think, feel, believe and do
Whereas conditioning is about creating a desired behavior, it is often desirable to eradicate other behaviors. This is called 'extinction'.
Behavior that have been created may become extinct if they are not fully maintained.
At any time, a response has at best a probabilistic correlation with stimuli. A loud noise that has been associated with pain will very likely cause a person anguish, but is not 100% certain in all cases.
If the stimulus is not applied and the response thus not generated over a long period of time, then probability of conditioned behavior happening will decay in a given pattern. For example the person who has not heard the loud noise for some time would not experience as much discomfort as they would soon after conditioning.
An important factor here is that conditioning must be maintained, with sufficiently frequent rehearsals and re-stimulus-and-response, for the pattern to continue over time. This implies that the underlying persona is not changed at a fundamental level, and that conversion, for example, is not a one-shot activity and requires constant attention.
Predictability of stimulus
If the condition has been created with regular and predictable reward or punishment, then the absence of the reward or punishment will quickly lead to extinction. If, however, the reward or punishment has been applied irregularly, then a second condition has been created where, upon receiving the stimulus, the person forecasts and imagines the reward or punishment being applied.
This situation takes longer for the pattern to become extinct, as the person is now maintaining it themselves, without external stimuli. Eventually, by accident or trial the person will find that the reward or punishment does not happen and thus the behavior gradually becomes extinct.
This is one reason why gambling is so addictive. The uncertainty as to whether the person will win or lose gives opportunity for prediction (and hope) of winning.
Another way of making a behavior extinct is to help the person become accustomed to the stimulus and hence not find it frightening or stimulating in any way.
When a person receives a stimulus and experiences the conditioned response a number of times, then the intensity of the emotion they feel may well become dulled with familiarity. This is used in therapy for example by starting with a weak triggering, and increasing the stimulus at the speed at which the person becomes desensitized.
This is also apparent in the use of pornography. A person who is stimulated by a pornographic image will find that it soon has less effect than it previously had. This leads them to seek to capture the experience with further images, and sometimes yet more erotic (and even illegal) tendencies.
Inoculation is a simple method, analogous to medical inoculation, where you present a weakened form of the experience such that the person finds it easy (and even laughably so) to resist a simulated 'attack'. When faced with the real situation, then they remember how easily they defended against the weak attack and so are better able to handle the real thing.
A strange thing that happens sometimes is that a behavior may become extinct not through ignoring the triggers that cause it, but actually exacerbating it to the extreme.
Pavlov found, with his discovery of the three stages of breakdown, a fourth stage, where dogs faced with near-death experiences 'forgot' all of their previous conditioning (and it took Pavlov several months to reinstate them).
This is used in therapy, where it is called flooding. A stimulus is constantly applied and more extreme responses encouraged until there is a sudden reversal and the stimulus no longer has any effect.
Aversion therapy uses the methods of conditioning to break a conditioned experience. Thus a behavior that is not desirable is punished when it appears. In therapy, techniques such as electric shocks have been used, and are understandably controversial (if you have seen Stanley Kubrick's 'Clockwork Orange' then you will appreciate the potential effects). It is not clear the extent to which aversion therapy works at all.
If you want to eradicate a behavior, you can either ignore it and hope it goes away, or you can deliberately use desensitation or flooding methods - be extremely careful with flooding (it is not recommended except by psychological professionals), as done wrong it can simply worsen the situation. Don't bother with aversion methods - they are not reliable and could cause moral backlashes.