This scenario needs us to read two layers from the vignette: where the smoker sits in the process of behaviour change, and which belief is holding him back.
On the process axis, Mr X is no longer ignoring the issue, he is weighing up whether to stop. Someone who is seriously considering change but has not committed to a plan is in the contemplation phase, which lies beyond precontemplation, the stage where a person has no thought of stopping at all.
On the belief axis, his hesitation is driven by the fear of becoming irritable after quitting. In the health belief framework, an anticipated unpleasant consequence of taking the advised action is a perceived barrier, often phrased as the cost of the behaviour. It is distinct from perceived susceptibility, which would describe how vulnerable he feels to smoking-related disease.
Putting both together, he is contemplating change and is restrained by the perceived cost of doing so.
\[\boxed{\text{Contemplation and cost}}\]