Guinnephobia

An irrational fear of Guinness alcoholic beverages, often accompanied by a response of denial, confusion and/or anger when exposed to sight, smell, taste or mere mention of a branded beer or other product. A Guinnephobe is a person who suffers from Guinnephobic traits or tendencies.

You can't even mention Guinness around that guy without him going off on you... He must suffer from Guinnephobia!