Let's just imagine (for the sake of an argument) that you're just about to be given a roadside alcohol breath test by a police officer, but in this universe hav

Let's just imagine (for the sake of an argument) that you're just about to be given a roadside alcohol breath test by a police officer, but in this universe having just eaten fish or chicken can cause a false positive. The officer asks you if you had eaten fish or chicken recently. In fact, you had both fish and chicken in your last meal an hour ago (don't ask). You should answer "yes". Most cases where "or" is taken to mean xor are actually asking for a choice, expecting one of the options as an answer. If the "or" is part of a question expecting a yes/no answer, then it is much harder to justify it being an xor.