Episode #4.6 - S4-E6
Stupidity: This is another episode when with a very limited number of suspects, not checking the phone records makes the case more complicated than it would be, but more importantly, the bad guy keeps the phone used for the shady affairs constantly switched on for no reason. No attempt is made by the police to trace the area it comes from, either - in fact it's very naive of the Commissioner to even try to call the number - but it works.
Episode #4.6 - S4-E6
Stupidity: The police finds a message the victim recorded on the phone. Conveniently, there is no timestamp on the message; it's a vital clue and with a modicum of effort surely a date of the recorded file could have been determined - but of course it would have made the mystery easier.
Answer: Most likely they had only tropical exotic drinks, he wanted an old fashioned English beer.