Dub (since the C gates all all but closed.) Lhr (no explanation required!) and Cwl are the worst for me. CWL security are the snottiest I've come across....worse even than those in LAX, which takes some doing.
Their route development is appalling also. Sitting waiting for the 'late departure' to DUB is depressing...nothing is open. Reminds me of DUB in the 80's!!