Why does everyone have such a problem with Heathrow? Yes, it's big but they have these wonderful yellow things with black text that help you find your way around...only an utter simpleton could ever have a problem doing an airside transit at LHR.
And don't get me started on US airports (that are strangely absent from this list
) that make you queue to check-in and then queue
again to get your hold luggage screened....and that's before you get to the TSA point....aaaarrgh!