Final answer:
The defence mechanism at play when a habitual drinker claims they drink alcohol just to be sociable is known as rationalization, where they justify their behavior with acceptable reasons.
Step-by-step explanation:
The defence mechanism described in the situation where a habitual drinker insists that they drink alcohol with friends “just to be sociable”, despite not caring for the taste, is called rationalization. This is a process where the individual justifies their behavior with socially acceptable reasons rather than acknowledging the less acceptable real reasons for their actions. By claiming the need to be sociable, the drinker is providing a logical excuse for the drinking, diverting attention from the real issue, which may be an underlying alcohol dependency.