Among examples of rules not widely shared among non-Christians that are enforced in present-day western countries, off the top of my head I can think of the ban on selling alcohol on Good Friday in Ireland

One could hardly come up with a worse example of a Christian-only prohibition. Alcohol is religiously forbidden to Moslems, and in some Moslem countries, legally forbidden on every day of the year, not just the selling of it, but the drinking. The punishment is flogging, or death for persistent offenders.

ETA: Ah, you said Western countries, which currently excludes all the Moslem states. But the Moslem populations of the West still have the religious prohibition.