Episode #3.7 - S3-E7
Stupidity: Humphrey picks the gun from its case using a pen to avoid leaving prints (since for some reason he's not wearing gloves), but then starts messing with the box with his bare hands without having it dusted for any print. Since the box was owned by only one person and hidden under his bed, any other print would have been important evidence. (00:11:40)
Episode #3.7 - S3-E7
Stupidity: The detectives suddenly bring everything to a dramatic halt to have a word with Joseph, because Fidel has been able to check the prints and his were the only ones on the gun and therefore he became really suspicious. It's his own gun, and people can wear gloves - in fact they do all the time! The fact that they automatically turn on him and he is unable to defend himself is simply 'because the plot this time says so', since in every other episode Joseph's prints would have been exclusion prints - they are supposed to be there and there's nothing suspicious about it.
Answer: Most likely they had only tropical exotic drinks, he wanted an old fashioned English beer.